I think this is the key phrase in what you've written. Quite often I've seen teams insist on separating things that cannot be released independently due to some form of coupling.

You end up with people talking about a particular "release" but not really knowing 100% what's in it and then discovering later that something is missing or included by mistake.

IMHO it's much easier to keep it all in a single repo and use the SHA value as a single source of truth when discussing what's in it. I don't really work on huge codebases though so your mileage may vary.