One problem I have with PFF is, aside from the obvious superstars, player grades never seem to track from season to season. This can happen, don't get me wrong, but it seems that a top-20 player one year will be a bottom-20 player the next, and this happens constantly. That strikes me as a lack of continuity with grading, since it seems far less likely that a player's skill level suddenly changed over the course of one 16 game sample to the next. Meanwhile, the superstars (or the players whom PFF has established through narrative are "underrated superstars") always are the top or among the top players at their position year to year, even during down years (see Revis in Tampa). To me, this seems to be grading to fit a narrative for certain players and total lack of any sort of a rationalized grading rubric for everyone else.
I think PFF can be useful if taken with a grain of salt but I see that year-to-year fluctuation with non-superstars constantly and it makes me think it's more about the people awarding the grades, which are of course just numeric stand-ins for qualitative analysis, than the players themselves.
