Well, I've been doing some research these days and apparently the Peak PA is the maximum PA reached along the player's career, i.e., the max PA reached in older versions of FM.
The issue here is that Peak PA seems to not work very well with negative PAs, hence the 247 of Nakai.
So, yes, something is broken, and can't be fixed trough the database, but it doesn't affect the game in any way. Nakai's PA keeps being -9, and that 247 can be fully ignored.
I hope this settles the matter...