@iCARRY That's what I love about this place. So much great info/history. Most importantly, is the grill in your trunk yet?
@Bob BQ Pretty interesting info. From your post it seems like the box pic you found would be an F. Any pics of the actual grill? I'm curious if the legs are black or chrome.
Putting all of that info together:
SJ-100 - Early models, prior to A-Code (1979 catalog shows model number 10001).
#10001 - A-Code through E-Code
#10001 / 50012 - F-Code (being a transition year)
#50012 - G-Code through sometime before M-Code
#10020 - Any idea when that started to be used?
At some point it looks like Weber reverted back from #50012 to #10001. Here is an example of an M-Code(1990) box that it labeled #10001. I have a picture of an N-Code(1991) which is the same box and N was the last year of the loop legs but do not have the angle to see the number.