I think we all know that Innova's discs have a tendency to change slightly over time due to differences in the plastic used, which mold, what time of year, was it humid or not, hot or cold out, etc. etc.,
So, even though it might just be two different guys marking the discs, there might still be a corollation (sp?) between the different markings and a difference in the discs. What if, say, one of them works the day shift, and the other works the night shift? Could that cause enough difference between discs of the same model that you would notice a difference in the flight pattern or wear characteristics?
Or it could just be your weird plastic "fetish"