Is this a possible sign of a refin?
IF the original finish was removed with a chemical stripper, could well be.
Wicking would explain how it got inside the F-holes, and the spot could be a drop of the solvent with dissolved NCL in it which then dried again to that whitish look.
Another thing I notice in that blow-up is what appear to be fine sanding lines visible at the edges of the reflection.
Somehow I think Guild would've taken care that that kind of thing didn't show up in an original finish by using a finer finishing grade of paper or possibly even steel wool.
Also enough layers of lacquer with proper buffing between layers should have helped make that kind of stuff invisible.
I'd trust Davisman's ideas about that, based on his experience in furniture refinishing.
It just occurred to me that the micro-scratches could also be the result of poor polishing technique and/or materials, that could be another explanation for the residue.
Maybe even more likely.
Maybe tried to use an auto-type polish with a little bit too much cutting power?
Also:. micro-fiber cloths are NOT good for NCL.
The fibers are actually harder than NCL so can also cause that kind of damage.
Most compatible with NCL since after all it's almost pure cellulose itself:
Plain ol' (clean) white
pure cotton t-shirt, and change it when it's dirty.