Anybody knows the difference between IPC-2221B and IPC-2221C?

[Relaxe]

IPC seems to have released IPC-2221C

When I see people talk about 2221B, it's mostly negative comments.
Did they change a lot with revision C?
I have found nothing about it online...

I'm mostly interested in clearance and creepage  for high-voltage in internal layers, as IPC2221B is the only place where guidance about that is provided, that I know of...