The grades dont change, If a group of pelts that was sorted from one collection is reconsigned to a different collection of course they will be sorted into that collection where they fit/match best.
Every year in fact every sale the collection varies.For example one year rhe marten may have an overall wooly finish and other years or even an earlier collection the species will have a better guard hair finish.
This is noticeable to experienced graders and pelts are sorted accordingly.
values and demand will also dictate how pelts of different grades are intersorted into lots.And so will the amount of fur per species dictate how many grades can be broken out.
But the grades dont change.
That’s a good way to explain it.
It’s hard for a new trapper, or one’s that don’t really pay much attention to the market/auction, to pick up what this paragraph is laying down.
It’s all good, but some get upset when they see their grades and don’t really understand the big picture.
Yup, to put it in easier English for the newbie to understand. The grades don't change, but the graders change where they sort the fur to match the current market and offerings.
So yeah, the grades don't change, but what the fur in that grade looks like changes from auction to auction.

And this isn't an FHA thing, the entire industry does it, NAFA did, Groeny does it, any auction that publishes grade sheets does it, and individual fur buyers do it.
And actual grades do change occasionally, but rarely. Kinda like language changes.