Hi @jk,
Yes, unfortunately, it is true that not all products allow you to add developers. What I am intrigued by is whether this functionality has really changed - is it really true that you could add developers to all products earlier (even if it was through the blanket route)?
Either way, it would be helpful to know which products you are trying to add developers to. I can at least give those teams a heads up about this gap.
Adobe Developer Console Team