I have a 1943 Colt M1911A1 with British proofs that I know was Lend-Lease. It is new and unfired except for factory and British proof firing.
The Lend-Lease program began in March 1941 and continued throughout WWII, sort of morphing into the various military assistance progarms at the end of the war.
The British proofs, BTW are not military proofs; few if any of those guns were ever issued because of the different ammo. The civilian proofs were applied when the guns were sold out of military stores in Britain. Some were sold in Britain (British "subjects" were graciously permitted to own handguns in those days) or the continent, but the bulk came back to the U.S. I saw them unpacked from the same crates they had been shipped in during the war.