Hmmm... all interesting suggestions. Thanks!
Looking through a loop at glancing angle to the film I still cannot say for sure which side the marks are on. In fact I don't see anything that actually looks like "debris" at all. What I can see is that these marks are very thin. I have a 50X measuring microscope and the marks are less than or equal to the smallest division on the scale, which is 20 microns.
The cinch marks idea seems quite plausible - I had some difficulty with a couple of these rolls as I was respooling them, and I may have in fact cinched it up as worker suggested. The static electricity is interesting too - I can see how that could happen cinching the roll (so maybe essentially the same effect?).
The lab in question uses a dip and dunk process - well at least I think they do. They cater to professional wedding photographers and I recall that they used to advertise their process as dip and dunk - so I can only think that they still do. Also, a couple years ago when I last used them for color negatives I don't recall ever seeing this effect. Consequently, I am starting to lean towards this being due to my own handling of the film rather than something at the lab.
I suppose that giving the lab another try, but this time with a 120 roll that I handle normally, would be a good test of the cinching hypothesis.