I've never gone by just the grommets as I have a newer repro that has split grommets. I always thought original Shell pp's had the Made in USA at the bottom, but that small type could possibly have been missed during original production on a plate or two in the 30's I would guess.
I hope we are not helping the repro people, as has been stated before on Old Gas, with pointing out what makes these repros incorrect so they can make a "better" product.
On the other more important hand, I know these posts are helping to save actual COLLECTORS, not decorators and the plethora of new fly by night "pickers", the heartache of paying too much money for a reproduction sign. I love seeing posts like this and hope that all the members of the site take advantage of this particular section of the forum. I know I didn't look at it for a long time and now know I missed out on tons of information by not checking it out.