It seems that Atmel have rationalized their datasheets.
It used to be that the 328P was in the doc8025.PDF and was marked as "preliminary". This always struck me as strange considering that the 328P has been out a while.
It seems now that the 328P has been moved into the doc8161.pdf datasheet together with the "PA" versions of the mega48/88/168. This says to me that the mega328P should really be called a mega328PA.AVR528: Migrating from ATmega48/88/168 and ATmega48P/88P/168P to ATmega48PA/88PA/168PA
explains the very small differences in the devices.