Yeah, I understand that. If the character was always there, unless there's a logical transition, I'd be thrown as well.

In one of my novels, I have a character who is often with his best friend. When he dies, the best friend takes over that portion of the POV, but with his own perspective, beliefs, and angst. It wouldn't have made sense for him to be a POV character before, but the reader already knew him and, I hope, finds the shift interesting because he isn't exactly as he appeared to the first man.

But usually, if I bring in a character late it's because they're not physically present and to make them so would be an obvious authorial device.

Cheers,
Margaret