>>4204940>>4204942>little chunks of silver halide fell off in developmentThat's a bit naive explanation, but either way it does look like film aging. See pic related and compare with
>>4202409 - both are from the same single roll, only shot and developed 12 years apart. It was deep refrigerated the whole time.
>>4204962Different stocks, different emulsion type, different aging, I don't think you can conclude anything from comparing one to the other.