If you created players prior to downloading and applying an online updated I think it deletes any previous rosters you had as before the apply there's a warning you will lose all unsaved changes. - It's annoying because if this is true, then every time you update the online rosters you have to recreate players and created teams. Though I just really started to create players, but the two players I created I lost before updating and had to recreate them. I'll let you know if I find anything different and/or a way around this.
So far though i've just saved the roster with my update #9 roster AND created players into one and my update #9 with no created players in another roster file, and will probably just adjust rosters moves manually if needed for the roster with created players.