I did a bit more research yesterday. I found an older thread on the CMP Forum that made reference to 15 rd. mags that were put up in 5 packs. Anolther reference mentioned 10 packs that contained (2) of the 5's. So far, I can't come up with any other evidence of individually labeled packages, other than what I've shown in my original post. Bill Ricca helped explain how the Stock Numbers changed from the late war years into the early 50's in this link:
http://forums.thecmp.org/showthread.php?t=94985
Another forum had a bit more on the (5) or (10) packs in this thread - reference to WB II is made in posts #9 & #10:
https://m1family.com/magazine-markings-t11.html
If you have WB II, look at the information on pp. 582-583. There are some corrections and additions on pp. 1306-1307 in WB III, but still leaves my original question unanswered. - Bob