It's hard to draw a line. Considering that google3 is a massive monorepo, where linking a library into any binary (or library) is just a matter of a single line in the BUILD file, a lawyer could argue that such binary is a derivative work (or, it could be a lot of work to argue that it isn't).

Also considering the internal-only patches to OSS libraries, it'd be at least a pain, and quite possibly a wide avenue for trade secrets to leak (not to mention that most of those are so specific to Google's highly specialized production stack that are useless to anyone outside).