I've posted before about old Kodak FB paper I've acquired over the years, most is from the mid 60's the rest from the 70's.
When I tested them all last year I was very surprised to find they were all usable giving reasonable contrast, good blacks, with no base fogging, only problem is they have lost a bit of speed and a little contrast.
I'm sure that variations in storage are the answer to this question, as, unlike Ian, I found that my old Kodabromide Gr II and III (Dark yellow envelope with a broad black band and white "Kodabromide" in the band) was junk. I had stored it underneath a few dozen active boxes/envelopes of Polymax FA and Elite. About 5 years ago (paper was 20 years old then) I tested it and threw it out. Darkroom vapors seep into paper envelopes and past the plastic inner bags. Time and humidity are cruel, but refrigerators can protect paper if the paper is protected from the refrigerator.
Buying old paper is a crap shoot and the dice are loaded.