What marks a collection as documentation?

We use Postman to publish collections. While trying to publish a new collection, we got the following error:

What makes it that one collections has documentation and another doesn’t?

I’m told that we have a limit of 25 published documentation, but we have way more than 25 published collections…

Turns out all published collections are considered documentation. The confusion being that only things published since October 1st, 2022 are counted.