Right. Again -- we're forming a personality on a newly blanked slate.
Take a chalkboard at the end of the day in a classroom and erase everything on it. Now try to reconstruct what was on it. Will it be exactly the same? Probably not. Handwriting may be slightly different, positioning will change. Even if all the text is same in terms of content, it's going to be different because of semi-random variations in how the i's are dotted and the t's are crossed.
Erase it and try again. And again. And again. Under the infinite monkeys theorem (weeb note: If you put an infinite number of monkeys in a room filled with an infinite number of typewriters and give them an ininite amount of time, one of them will invariably write the complete works of Shakespeare), if you repeat this process enough times, you'll eventually hit an exact match.
That's the process that Sensei has been going through since the jump. He wakes up, no memory, no idea where is or even who he is. He begins forming a personality. It's imperfect. Eventually, during a reset, he gets erased and the process starts again. Maya's been doing this a VERY long time, and she now believes that THIS Sensei is the closest she's ever gotten to a complete match of the original. That doesn't mean those other Sensei's weren't senseis. They were just imperfect attempts at reproducing his personality, not other people entirely. All the parts were there, the i's were just dotted wrong.