I developed some HP4 120 rollfilm a few years ago that had sat in my Dad's loft since the 1960s...

I contacted Ilford and they supplied me with development times. I'll find these and post them if you wish, although I supect they are of little use.

The base fog was very high, thus bringing the effective film speed right down and probably making a nonsense of any development times anyway - but I did get useable, printable images.

The bottom line is, do you have even fog? (nice and uniform, so the film is useable) or patchy and irregular? (in which case forget it unless it can be used for 'arty special effects'!) My film had lots of fog, but perfectly even, almost like it had been coated on a hazy, matt backing.