Those two cats are not identical. For example, Finnegan has darker markings on his right foreleg than the donor Frankie. The pale horizontal markings above the eyes appear to differ somewhat too. I’m sure with more extensive photos more differences would be apparent.
It was the great and underrated(*) genius Alan Turing who first conjectured how Zebra-like striped patterns arise naturally from random processes.
ETA: * - IMO. And I call him “underrated” even knowing he’s already rated very highly.