I doubt very much that pistol is unfired. The EXP's were made for testing.
Those were made about 30 miles from here, my aunt worked there building 1911's and later parts for the M1.
Approximately 100 EXP marked pistols made up from preproduction trial run slides, receivers, and small parts were used in various experiments at US&S. So it is a rare one and I doubt all 100 of these survived testing.
Different finishes were used on the EXP's. That one could be a Du-lite blued finish over a polished surface, the other finish variation found in this series of pistols was sandblasted and then blued.
US&S tested all of the 55,000 1911's made there on their own range, 21 shots were fired. And I think it has been said that not one failed the factory test firing. Well made pistols with a better reputation than the Remington Rand and Ithaca. The US&S pistols did real well on the governments test of disassembling 24 pistols, mixing the parts and putting them all back together to test parts interchangeability.
Only the Singer was made in lower numbers with only 500.
Value...I don't have a clue.
And yes John...I call that part the "dust cover" also. I don't remember where that came from.
EXP94 with sandblasted/blued finish.
EXP98 with polished/blued finish.