I know that fringed stipules can be a trait indicating Rosa multiflora somewhere in a rose's lineage, but I don't know much more than that, nor am I familiar, offhand, with the intricacies of Abe's heritage. "A little knowledge is a dangerous thing" :-), so hopefully one of our experts will weigh in. Maybe a sport/mutation that is allowing the gene/set of genes connected to fringing on stipules to be expressed?

That's an odd trait. I COMMONLY see it on "Old Town Novato". But the lady who discovered it, and who grows it in NoCal (far closer to where it was found) says she does NOT see it on her bushes.