I really enjoyed the Tom Laemlein article and the comments by the late Larry Ruth, who was a very good friend of mine. Regarding the idea that expended Carbine magazines were saved by GIs/Marines to be reloaded later, I can offer the following - very limited - observations. My service in the Navy and later with American Airlines afforded me opportunities to walk the battlefields of the Pacific and Europe with a metal detector for more than 30 years.
In all my explorations, I only ever found one expended carbine magazine, and it was in a cave on Okinawa; Perhaps accidentally dropped rather than discarded. The flash from firing a Carbine in a dark cave would've resulted in "flash bulb blindness" for a few moments.
Related thoughts: I only ever found one expended BAR magazine (in a foxhole in Germany), and a handful of loaded BAR magazines in a foxhole on Okinawa. My thought was that the latter guy - a Marine - was wounded and evacuated or killed.
I've never found a Thompson (nor M3 submachine gun) magazine, although I found lotsa .45 spent casings and live rounds. Were those Marines/GIs saving their empty magazines also? It seems likely.
The 1945 retaking of Corregidor was an airborne operation with lotsa Carbines, but although I found plenty of ammo (both spent and live rounds), no magazines were found (at least not by me on the one day I was there.)
Both expended and full Garand clips were commonly found in both Europe and the Pacific, but of course Garands were more widely used than Carbines, BARs, or Thompsons/M3s.
For what it's worth, one person's very limited observations.
Regards, Marty Black