Mystery Players On My Roster To Start Season

The last two seasons, I have opened up my roster to find between one or more 3* added to my roster that I had never heard of. Usually they are older (26+). I assume I'm not the only one seeing this. Not that I'm complaining, but I am curious how/why this is happening.

They could have replaced somebody who had retired.

retirements probably left your squad short. so the game chucked you a few generated or unassigned players to make up the numbers

Makes sense I guess