Hi Scott,
The Gibbs US Standard series stirred up quite a turmoil as OC always having the Govt. Contract and Gibbs getting it away from them was virtually unheard of. The Gibbs U S Standard series was produced somewhere in the years running from around 1931 to around 1936, as in 1936 ATC bought out Gibbs. The production totals I have never seen on the U S Standard Series.
Was the trap you saw a #4 or #4X? The true #4X Gibbs U S Standards, which was the competition trap to the Newhouse #14 is a tuff one to find. The #3 and the #4 of that series are easy to come by. The problem is with the #4X the high value trap in the series it is also a trap that is faked. The #4 sets farther to the left on the #4X than the #4, and there are many unscrupulous trap doctors out there that will take a #4 U S Standard and stamp or needle an X in back of it, put a set of Newhouse #14 jaws in it and sell it for a Gibbs #4X.
Now, after ATC bought out Gibbs and were using up parts, you may find Gibbs parts married with ATC parts and have a trap that is factory right, but not a pure trap that was made during the Gibbs era. Buyer definitely beware on the #4X Gibbs U S Standard. This was from Nhousecattrapper