The Government Printing Office (GPO) document, Digital Distribution to Depository Libraries: Exploring the Issues (9/6/2006) asks these questions about Selectivity:

5. Selectivity
a. When can a selective library / regional select only the digital version of a publication?
b. Are there exceptions?

Q: a. When can a selective library / regional select only the digital version of a publication?

A library may select only the digital version of a publication provided they have a backup and/or preservation plan for their digital publications subject to the exception below.

Added 5pm 10/18/2006 - We'd like to be clear that we feel that selecting a digital item to be downloaded to a library's servers should not preclude that library from selecting a tangible format as well. We can envision times when a library would want both tangible and digital: one for easy access and searching, one for presentation/preservation and a different kind of access!

Q: b. Are there exceptions?

When the tangible format is a legally controlling version, then the tangible version must be selected.