M1928A1s would have been reasonably common in Europe. Some units that had been overseas since 1942-43, like 2nd Armored Division, had plenty of them because M1 Thompsons weren't even being made until nearly halfway through 1942, and either soldiers kept the 1928s themselves, or they were reissued within the unit.

The US Army in Europe was at the end of a 6,000-mile supply chain. Combat units didn't have the luxury to throw away a perfectly usable weapon just because the newer model showed up. M1928s were considered a standard submachine gun through the end of the war in Europe alongside the M1/M1A1 Thompsons that eventually outnumbered them, and the relatively few M3s that trickled in late.

Here's Ronald Speirs with one in late 1944-early 1945. This dude in France has one in 1944. Here's Churchill trying one out at a firing range for an American unit in March, 1944. If you take a good look at photos of soldiers in combat carrying Thompsons, sometimes a surprising number of them are 28s.