So my understanding with managers is....you can make them playable on retail but not selectable, thanks to the change in 2k17 where there is no longer a "Divas" menu to select from. The only way to be sure you select them is via royal rumble or hitting random and getting lucky.
2k16 and prior you could select Managers that were made playable via the Divas menu trick that I discovered years ago.
should be noted there are a lot of garbage NPCs referenced, but not actually playable as there is no model for them(so they crash the game when you try to play as them) and playing as the ref can crash games as the ref moveset is buggy. But there are random NPCs through the series that appear. 2k16 had "press start button" as DLC character lol(the Xbox one universe mode would occasionally glitch and feature this "Press start button" in matches lol) and Renee has a full model in 2k16 and I think 17 despite appearing nowhere in those games. Also many characters that were usable in the old create a story mode like doctors and trainers among others, are still inexplicably on the disc and can be made playable.