Sandy,
I'm currently going through a box of 5x7 HP5 that expired in 1996, and it has just a teeny weeny amount of base fog above normal. It's working very well indeed, and I can't see much difference in image quality compared to fresh film.
I develop with continuous rotary agitation, using HC-110 developer, 500ml / 2 sheets @ 1+100 dilution, for 9 minutes.
I have a box of FP4 from the same period, and it works like a charm too. I also have about 60 rolls left of Plus-X 120 that expired in 1996. Those look fantastic in both HC-110 and Rodinal. For some reason or another I can't get it to work with Pyrocat or Edwal 12, but that's a different story.
The best story of them all is a box of Kodak Tri-X 400 4x5 sheets that expired in 1983. Believe it or not - those turned out really nice in Pyrocat.
Then, of course, I've had a few duds too. And I think some of it were the same brands as above. Storage conditions seem to be the common denominator.
Stored well, I think b&w film can definitely keep for a long time.