Ive heard that having multiple SBR uppers for a single registered lower on a form 1 is acceptable. The only condition is that the subsequent SBR uppers must have barrel lengths that exceed that of the originally registered SBR on the form 1. So if i register a 10.5" barrel on my form 1, i can buy other larger SBR uppers, for the registered lower, as long as they are greater than 10.5". Is this correct? Thanks!