as always it depends, I never ever stored paper in the fridge. Last weekend I took some sheets ADOX MC110, which is a multigrade fb paper, and made some photographs.
Checking for exposing values I took the index value I measured in 2010, I know this 'cause I've noted it on the package.
It's 8 years old and stored in my basement where it has not more than 17°C during the whole year.
I also had AGFA Provira paper from 1960 and could use it very well, Ian I think you have one sheet

But I also bought some packages on flee markets and they are only grey an dull.
But well it's easy to check, make a simple test print a you see what you get.
Don't pay too much for old paper, you'll waste too much time for it.