There is a lot of space between (1) a copyright notice, (2) a valid copyright, and (3) a valid claim against a third party for copyright infringement. On (1), authors can attach copyright notices to their work, but it isn't necessary to secure their copyright interests, nor is it sufficient to make the work protectable. On (2), validity will depend on whether the work is protectable expression and whether or not the expression merges with the idea. On (3), there are a whole host of defenses to infringement including Fair Use and a de minimis defense (copying is so small it doesn't matter).
Here, I'd expect that an expression of an empty program would merge with the idea of an empty program, which would make it not copyrightable. Of course, that doesn't stop someone from putting a copyright notice on it anyway.
I'd like to emphasize that a copyright notice' purpose is to serve as evidence, should a copyright claim be made. As you said, it is neither necessary nor sufficient to establish a copyright. There's no harm in putting a copyright notice on uncopyrightable material. With that understanding, including a copyright notice just makes sense.
If you're AT&T you have two options. You can tell your engineers to just always include the copyright notice, or you can ask your engineers to understand copyright law well enough to decide whether the notice is called for. The decision is pretty obvious.
EDIT: Ohh, there is a third option. You can pay lawyers to review every code file.
Here, I'd expect that an expression of an empty program would merge with the idea of an empty program, which would make it not copyrightable. Of course, that doesn't stop someone from putting a copyright notice on it anyway.