question about the grading system

i know the grading system takes into account how well you did for your role vs players on the same skill lvl on that champ.

but i do have a question...

with buffs and nerf a lot of champs and champ going from OP picks early in the season to worthless picks now.

how often does the grading system take into account NEW stats.

for example..

got a HUGE rework, and likewise it probably changed ALL his statistics.

other champs like have gone form S tier to trash tier.

but if you are trying to get your lvl 6 or 7. are you being compared to the champ in THIS patch?

or is the game still taking into account the champ how it was when it was OP during the pre-season?

how far back does the mastery system look when comparing you to other players?