I've just noticed that Chico Cois has all stats at 10. This seems to have happened during the "Cannons of Mona" part. I've got a savegame when I was at Hopital, on the way back to Havana after the mission, in which Chico has most stats at 10 and a couple at 9 plus stupid percent ("stupid" means "several hundred"). And another from just before I was going to Isla Mona, in which his stats are rather more sensible and only a few are at 9 or 10.