Jay, here we just disagree. Not only do I grade differently based on age, but also on type of poster.
For example, most Australian daybills are in pretty nice condition, so I grade them on a very tough scale, or else you would see "very good to fine" or "fine" on just about all of them.
And Mexican posters are mostly in lousy shape, due to the paper they were printed on, with many brittle and brown. So I grade them on a more lenient scale, or else you would see "fair" or "poor" on just about all of them.
And grading one of a million BLADE RUNNER one-sheets on exactly the same scale as one of the two known THE GOLD RUSH one-sheets just doesn't make sense to me.
It seems to me that this helps collectors more than using an "absolute" scale (and of course I make it clear that this is what I do, and that is vital to doing this).
Bruce