Quote:
Couldn't a "jumbo" be cut and certified and actually be a fake?
You'd have to overcome a lot of skepticism to get that good cert. Expertisers will approach every submitted putative #315 with the null hypothesis that it's a trimmed fake,
unless it truly is obviously genuine (comes as a pair imperf between, for example). From their point of view, it's a lot better to return "no opinion" on a genuine 315 than to give their imprimatur on a trimmed fake. So any stamp with borderline 315 measurements won't get the nod just because of measurements. (Ample 315 measurements won't get the nod immediately either -- you have to check for paper added at the margins.)
There are other things. Another thing they will look at, for example, is how the stamp was separated. If it was torn, or there was one clean scissor/guillotine cut, that's good; that's what they expect to see. The edges will be examined under a microscope. If there's
any sign of filing, sanding, or cutting with an X-acto knife, or similar, it's going to be called fake. If there are any remains of perf holes -- or any bevelling that might be the
edges of perf holes -- then it will be called a fake as well. If they can't tell how it was separated, that's a good excuse to return "no opinion".
It will be hard to obtain sufficient measurements, BTW, from a trimmed jumbo, at least if you trim with scissors (use anything else detectable under examination and it will likely be called fake.)
I'm not an expert in this issue, so there might be other tell-tale signs that differ between the issues (paper thickness, for example.) But just close examination of the edges will rule out many trimmed fakes.