A lot of stamp happy workers in that factory. Note the divots in the bb shell where the chain stays go in. Many mass production frames are assembled in a jig, "Nailed" together while in alignment, then removed for brazing. Raleigh literally used a drill and then a small nail to hold the bits together. They would put small rings of brass in the lug prior to assembly and use wide torches held in place to melt the brass. I'd guess the motobecane method was cheaper and faster. We can see the brass in the lugs suggesting they were brazed in a more typical method. The bb shell and lugs are press steel lugs so they are soft enough to dent or nail through. No cast steel lugs on these cheaper bikes. The factory paint would hide many of those numbers. Interesting archeology revealed by striping the paint. You might consider just clear coating the frame.