I keep planning to do sensitometric tests to prove it but...
I still believe slow black and white film keeps indefinitely. For example I still shoot Panatomic-X of unknown heritage that I bought on an auction site and put in the freezer. I cannot tell the difference between vintage (shot and developed while fresh) and current negatives (shot now and developed now but expired '84).
My hunch is that gamma rays affect slow film less than, say, a 400 speed film. The key (my un-scientific hunch) is to shoot and develop reasonably quickly so the latent image doesn't fade. By that logic I imagine a vintage photograph (shot while fresh in '84 and developed now) would be 'worse' than a fresh shot developed timely on expired film.
ps I work for Kodak but the opinions and positions I take are mine and not necessarily those of EKC