iserlohn was originally supposed to possess the corpse of the previous doctor (which makes them two separate people) but the writer whom i commissioned his first fic from suggested that he should be the doctor from the beginning (so he didn't bodyjack a stranger), and i've rolled with it since then. originally the memory loss was because he doesn't inherit the memories of the corpses he used as a host but now it's because the original doctor was an autonomous clone that he sent to Terra to scout it out and lost some of the data recorded inside