I believe he was more human - or perhaps we should say more sentient - than he even thought. I remember the episode Brothers
which featured Brent Spiner as Dr. Soong. When Soong is dying, Data says something about not being able to mourn him. Even Soong, his creator who presumably knows Data's capabilities more than anyone else, makes a coment that he actually will be able to grieve. I don't remember the exact words. I'm sure someone can clue me in to the exact dialogue.
Anyway, to me, that means that there is a lot more to Data than ANYONE gave him credit for.