Thread resurrection! I have similar symptoms with 20-year-old 70mm Tech Pan - see my post here and scroll down for the image sample.
Given that I've received some tech pan that has evolved so far that it'd be legally allowed to vote, it would seem to support the notion that the original poster here also has something growing on their film.
In my case I can tell you for sure that it's not double exposures; I made my series of exposure test shots using film loaded directly from a factory-sealed Kodak box. In my case, you can barely see the fungus (?) on the surface of the film outside the image area but it has no silver density there. It's only where fungus AND optical exposure occur together that the effect is visible, as if the fungus is acting as a development catalyst.
The patterns are a little different on mine too.