the 'look'

I'll go out on limb here. Even without a proven provenance, some jackets are undoubtedly correct because of other things. For instance, if you have a jacket from a non-nondescript unit that has been in your collection for thirty years, odds are it's authentic. I'd also suggest that even cloth gets a 'patina' or look that only time and wear can provide. If your recently bought e-bay jacket from a desirable unit lacks this, then I'd be skeptical. If, on the other hand, a jacket turns up that is correct in all the check-able areas, and somehow 'looks right', that may be the best evidence you'll be able to come up with that it's legit. If I were to demand guaranteed provenance for all my tunics I'd have probably a third of the ones I now have. The odds of the other 2/3's being modern made up jackets is remote given the wide variety of sources they've come from. On the other hand, if the patches just don't appear to have been attached all that long, or if weathered flashes are on a stiff new tunic, I'll take a pass.