Is it permissible to make digital copies of choral music that is legally owned by the institution to students in choral and instrumental ensembles? Some students may be studying remotely and mailing physical copies may result in lost or non-returned copies.
There are four ways it can be permissible:
1. Check the license from the publisher and see if the purchase of the physical copies came with any digitization/duplication permission. You'd be surprised how many rights you buy (or don't buy) when you make that hard copy purchase. Publishers take a variety of approaches on this, and an individual publisher's permissions may change from work-to-work, so confirm (or rule out) this approach for each work.
2. If the license does not allow making digital copies, contact the publisher, and see if it can be expanded. Publishers are now getting many requests like this and may be ready with a simple (and affordable) solution.
3. I am not a fan of them (they are as outdated and as risky as the Ford Pinto), but the "CONTU" guidelines speak to this issue. I am including the relevant guidelines, as presented in Copyright Office Circular 21, under this answer. If one of your precise needs fits one of the "permissible uses" listed in Circular 21, you are all set.
4. Speaking of CONTU, the first "permissible use" listed in the guidelines may help you out here, with a slight twist on your scenario. In the event that the physical copies listed in the question are mailed out and not returned as feared, the guidelines allow for emergency copying after the fact (of course, they also require that at some point, you purchase more physical copies, but at least you can get the copies to the students).
Those are my four solutions, based on conventional approaches and current case law.
I'll also throw out a "fifth option" based on a slightly different approach, which, depending on some precise facts, could work for faculty teaching choral classes:
The 110 Solution
Copyright Section 110 allows an academic choral group (if meeting as part of a class) to display "a work in an amount comparable to that which is typically displayed in the course of a live classroom session," during an online class/rehearsal.
How can that help with the member's scenario?
If the class was still meeting physically, Copyright Section 110(a) would allow us to perform the song and to display the music on the in-class smart board. In the online environment, the same performance and display could happen via the internet, as allowed by 110(b) (the "TEACH Act")—again, so long as only the amount "typically" displayed in class was shown.
Whether in-person or online, the rehearsal would include review of the different parts for bass, tenor, alto and soprano, with the relevant music displayed on the screen. While an academic institution can't tell people to take screen shots of the music displayed for rehearsal purposes, students who want to snap screenshots of a class to take notes is a fact of modern-day academia. If a student who was told to purchase a copy of their part uses this method to ensure they are practicing on an incremental basis, that's out of the school's control, and the student can make their own claim to fair use.
This type of solution should never be used as a deliberate alternative to the purchase of individual copies. But so long as the display is incremental and truly a part of the in-class experience, it is a viable option.
I wish all music faculty approaching the Fall 2020 semester many good performances, whether virtual, or face-to-face. These are tough days for people who love to sing, who enjoy the community of a choir, and who need to hone their vocal art in collaboration with others. Hunting for music should not add to the burden, and with a few tricks and an awareness of the limits of the law, it doesn't have to.
Guidelines for Educational Uses of Music
The purpose of the following guidelines is to state the minimum and not the maximum standards of educational fair use under Section 107 of H.R. 2223.
The parties agree that the conditions determining the extent of permissible copying for educational purposes may change in the future; that certain types of copying permitted under these guidelines may not be permissible in the future, and conversely that in the future other types of copying not permitted under these guidelines may be permissible under revised guidelines.
Moreover, the following statement of guidelines is not intended to limit the types of copying permitted under the standards of fair use under judicial decision and which are stated in Section 107 of the Copyright Revision Bill. There may be instances in which copying which does not fall within the guidelines stated below may nonetheless be permitted under the criteria of fair use.
Reproduction of Copyrighted Works
1 Emergency copying to replace purchased copies which for any reason are not available for an imminent performance provided purchased replacement copies shall be substituted in due course.
2 For academic purposes other than performance, single or multiple copies of excerpts of works may be made, provided that the excerpts do not comprise a part of the whole which would constitute a performable unit such as a section¹, movement or aria, but in no case more than 10 percent of the whole work. The number of copies shall not exceed one copy per pupil.
3 Printed copies which have been purchased may be edited or simplified provided that the fundamental character of the work is not distorted or the lyrics, if any, altered or lyrics added if none exist.
4 A single copy of recordings of performances by students may be made for evaluation or rehearsal purposes and may be retained by the educational institution or individual teacher.
5 A single copy of a sound recording (such as a tape, disc, or cassette) of copyrighted music may be made from sound recordings owned by an educational institution or an individual teacher for the purpose of constructing aural exercises or examinations and may be retained by the educational institution or individual teacher. (This pertains only to the copyright of the music itself and not to any copyright which may exist in the sound recording.)
1 Copying to create or replace or substitute for anthologies, compilations or collective works.
2 Copying of or from works intended to be “consumable” in the course of study or of teaching such as workbooks, exercises, standardized tests and answer sheets and like material.
3 Copying for the purpose of performance, except as in A(1) above.
4 Copying for the purpose of substituting for the purchase of music, except as in A(1) and A(2) above.
5 Copying without inclusion of the copyright notice which appears on the printed copy. (iv)
Discussion of Guidelines
The Committee appreciates and commends the efforts and the cooperative and reasonable spirit of the parties who achieved the agreed guidelines on books and periodicals and on music. Representatives of the American Association of University Professors and of the Association of American Law Schools have written to the Committee strongly criticizing the guidelines, particularly with respect to multiple copying, as being too restrictive with respect to classroom situations at the university and graduate level. However, the Committee notes that the Ad Hoc group did include representatives of higher education, that the stated “purpose of the … guidelines is to state the minimum and not the maximum standards of educational fair use” and that the agreement acknowledges “there may be instances in which copying which does not fall within the guidelines … may nonetheless be permitted under the criteria of fair use.” The Committee believes the guidelines are a reasonable interpretation of the minimum standards of fair use. Teachers will know that copying within the guidelines is fair use. Thus, the guidelines serve the purpose of fulfilling the need for greater certainty and protection for teachers. The Committee expresses the hope that if there are areas where standards other than these guidelines may be appropriate, the parties will continue their efforts to provide additional specific guidelines in the same spirit of good will and give and take that has marked the discussion of this subject in recent months
 Checking a license is not an exact science. Some publisher's use a catch-all that is included on their invoices. Others put the information right on the music. Others like to make you really hunt for it, but it is usually part of the sale transaction. This is why, when making a purchase of music, it is good to take a screen shot or save the paperwork related to the purchase.
 Note: To my knowledge this work does not exist, but it is on my wish list of music to hear. I love it when genres collide.
 This new version would be a "derivative work" based on the original, and have its own copyright protection as a musical composition.
 We have reached the limit of my choral knowledge. Is there separate sheet music for mezzo-soprano and counter-tenor? Probably. I am sorry, I quit choir in 7th grade.