As to the last question, you answered it, how much needed = minimum amount of magnification needed to discern and distinguish an airbrushed SS faux "decal" from a real celluloid based decal/transfer. The next question is this: my understanding of magnification, particularly microscopes, is that they've been around in one form or another very briefly, like only 600+ years, so is it understandable then why it took over 40 years for anyone to do a magnified/microscopic study of the Champagne Rune "decal"? Had such an objective analysis been done in conjunction with an SS book project, say by a semi-pro with help from someone experienced in decal applications and airbrushing (e.g., a graphic artist or good body shop striper) do you think it would have definitely revealed these as airbrushed humpjobs selling for $4500 to $24,000 long ago? Is it possible for someone, particularly an author writing a book on SS helmets, to simply examine one of these under high magnification once a controversy started brewing? Would that be very expensive and time consuming? Probably no more expensive than renting a $25,000 handheld XRF and tazing hundreds of helmets and collecting data from around the country? Would you think someone prudent would do this after credible evidence was posted on a forum showing a $20,000+ SS double decal helmet may have an airbrushed faux "decal" on it? Thanks for your input!
Well 30-50x would let
you see whats going on, but if you wanted images for a book or article, then I`d say you need to get down to 60-80x, and again here, you`d need to be able to capture a fairy large area all at once at that depth, or at least be able to stitch together a few images in series to get a nice image.
You wouldn`t even need anyone with experience, as the detailed images would reveal how the item was created.
The only problem you would have, would be
if originals were airbrushed onto a thin sheet of celluloid.
But they were certainly not, they would have been transferred onto the celluloid using a different procedure.
So, whether that was screen-printing, tampondruck, offset, by way of a huge rubber stamp or even if each decal was handpainted onto the celluloid by a GESTAPO officer wearing a minidress, whatever, it will show you how it was created under high magnification.
So, if a decal is spray-painted, you will see this under magnification. If it is printed on a LaserJet printer, you`ll see it. If it was photocopied, you`ll see it. Simply because all methods are very different.
Maybe not to the naked eye, but under high magnification they would reveal themselves.
Reminds me a bit of the paper 1932 SA badge I exposed while back. (They are still selling as genuine even today) Printed on a desk jet using a printing method that was not even invented in 1932.
I have never handled a helmet, ever, apart from my motorcycle helmet, yet I would bet anyone, any amount of money they wished, that I would be able to correctly identify the way any decal was created. And I could show it in a matter of minutes, and prove it conclusively. What that would mean I don`t know, because I have no idea how period decals were made. (Maybe a GESTAPO officer wearing a pink mini dress did actually hand paint each one) But simple micro imagery would certainly show you quickly what the decal was.
The answer to all the above is no. What possible reason would someone, who has already made a name for themselves, need to be bothered by a stupid thing like microscopy. I know that it has saved the Art industry billions of dollars, and helps send people to jail around the modern world daily. I know that it has foiled banknote and cheque forgers plans for decades, but when it comes to Third Reich artifacts, this is not how it is done. Opinion and a good story take precedence over anything as trivial as forensic evidence. This is not X Files or CSI Miami, this is just a hobby, meant to be taken with a pinch of salt and one or two of Walter`s bulbs. There is very little common sense when it comes to swastika adorned items.
but apart from that there would be absolutely nothing to it.
Better still, just erase and lock the thread! 
It's funny how everything we said and predicted came true. We were far ahead of the time, and all it took was a little common sense and no censorship. It's hugely ironic that the Champagne Rune and XRFacts, which seemed to be argued by their proponents as mutually authenticating did just the opposite.