You can import historical players. You can do this one at a time or you can create a list in a text file to import a team or even the entire league. There have been multiple posts on how to do this. I have responded in past versions so try using the search function. Try my name in the search. Here is a text file I used to import a team. I suggest to do one team at a time.
http://manuals.ootpdevelopments.com/...orical_players