U.S. Army acceptance (inspector) marks should be present on all the M&P's that were bought by the U.S., which means all guns of either caliber made after about mid-1941. That was when the Lend-Lease program (signed into law in March 1941) reached the factory level. So those later guns were technically being made for the U.S., where prior to that they were made for the British or other countries under direct contracts with the purchasing country.
The term "Victory Model" came about when serial numbers of the M&P reached 999,999. S&W's numbering machines only went to six digits, so they decided to use an initial letter which could be put on all the frames before the actual numbering was done. At first, they were going to use "A", but some one suggested "V for Victory", a common slogan at the time, and the later guns became "Victory Models."
Jim