They're for different size bottom row keys. The Majestouch PCBs have the same thing. The space can move a quarter unit to the left or right, I think, and you can move the entire bottom row on the Majestouch. The plate won't allow for it, of course, but I'd wager the PCB is almost the same for every Majestouch to save money (one PCB for ANSI-like and one PCB for ISO/JIS?)
Edit: Failed to read the whole thing!
Maybe they send different scancodes when the firmware is different?