I understand that certain companies are quite quick to remove posts about their software on the sister site (Sonible, Baby Audio, etc.). I also know that there are a couple other places that these posts may be posted to.

Usually the entire page disappears from the sister site quite quickly, so we might not even know the software was released in the first place!

Is there a repository that contain a list of all previous group/team released software?

There would be no grounds for companies to remove a list that simply contains text with the name of the releases (as opposed to actual download links), and it would be very helpful to users in case they missed something.

May already exist, and if it does, please let me know!

 

You want a predb for audio software like Upawg.ca was. Maybe there is one but not public, which has been not mentioned. But you are right, without one there are still other ways to figure it out, with some degree of accuracy depending on how far back you mean. It's not the same thing though.