was "guaranteed" that each sheet was to be usable ?
if not, its kind of like buy at your own risk i would imagine ...
paper i have gotten used has be unopened or out of date from
a source i can trust ( friend, client whatever ) or didn't cost very much
and purchased on ebay ( cheap 70 year old azo where it takes a lot of bright light to expose )
i hope you didn't spend much $ on this paper or that at least some of it mid-box or 1/2 way across each sheet
is usable for small contact sheets.
i wouldn't be surprised if the store says you are SOL ...