Indeed Mr Swan, you are correct but I doubt there are many after say 1000 if 1000 is a reasonable point. As we say here in Oz, a smidgen frames have gussetting after say 1000 which means few
I have no ideas as to why there are gussetted frames after say 1000, my only thought would be random selection prior to stamping, early frames being rejected for some flaw such as welding or alignment could be a possibility. I doubt we'll ever know. One of those mysteries I spose