Mounted as intended, mine lies back at 34° measured. (O, those magical phones!) I'm not going to switch it around again, so I don't know if the two mountings are different, but it's different from both of yours. I note the mount point isn't particularly strong, so I'm going to suggest that one or both of ours are bent a little. I'm glad you got yours working; it's a nice feature.

I have (or maybe had) an SG1 or SG3 with matching numbers on the frame and carriage, but I don't think it means anything in particular. They might have left the factory that way, or maybe sometimes not, in order to fill a certain order, but I don't think you can infer anything definite or definitive about the way we find them now. I have switched carriages and then forgotten about it, so what would that mean to a future owner? Some business got typewriters and then additional carriages for certain uses. Repairs, too.

The main use of serial numbers is warranty claims, inventory control, and ID of stolen items. It is of more concern in authenticating automobiles and firearms, where parts were not intended to be swapped and where it might reveal seller chicanery. Our main current use is determining date of manufacture. If one has matching numbers on separate parts, it is just an interesting occurrence, like finding consecutive serial numbers on eBay purchases eight years apart.

Thanks, Uwe !