I think you’ll find average female wrist sizes would fall in
category 6.5 but within that range you have a full inch encompassed.
An inch is a lot, a whole lot, too much to lump together in one
category, imho. Overall average size is 7 - 7 1/4. I’ll say from
experience that even that 1/4 inch sometimes means fit or no fit
(sale or no sale).
More meaningful would be measurements of width and thickness of
wrist for cuffs. Not only do you need a good fit once on, but you
need to allow sufficient gap to slip over narrower dimension of
wrist, which should account for the springiness of the particular
cuff and the shape of the gap ends.
If someone is in the cuff business, it might be good to make some
cheap size samples.