Do all the decks have identical deck backs?
First of all, Rumpp is likely the box manufacturer. It's not uncommon to sell nice storage boxes with another company's cards in them.
Assuming all three decks are the same, they're all USPC Congress brand, with a "U" date code on the AoS placing them as being made in 1955, consistent with what you stated. The look as if they were once gilded, but much of that gold has worn off with use. They're heavily soiled from use - are any of the cards damaged, torn, bent, crimped, etc.? They appear to be bridge-sized (dude, you have small hands)!
The vintage value on a soiled, worn set of bridge decks isn't very high. The box might be worth more than the cards, though.