I shot some HP4 a while back. It was circa 1960s... it had been stored in a loft, too, so had seen some big temperature fluctuations!
The result were... well, it was ok, but had a very high base fog and probablyless than half of it's rated speed.
Any idea how fast your film is? Slow films seem to last much better, whatever they do to fast films to make them fast also makes them fog much quicker over time. I tried a 1920s Wellington glass plate a few years ago and it was squeaky clean, fog free and looked as fresh as it did when new, probably... but it was only about 1/2 ASA!
Still, my HP4 gave me some printable pics, so good luck and let us know what happens.