Just my two cents, but the seat stays don't look like any Carlton I've ever seen- even when they didn't build their wraparound seat stays on 531 models, I've never seen stays that are flush with the seat tube like that, or stays that don't meet the tube right at the top.
To me that suggests it's either not a Carlton, or it's built to order, as you suggest.
Feel free to correct me though, more knowledgeable people.
Just my two cents, but the seat stays don't look like any Carlton I've ever seen- even when they didn't build their wraparound seat stays on 531 models, I've never seen stays that are flush with the seat tube like that, or stays that don't meet the tube right at the top.
To me that suggests it's either not a Carlton, or it's built to order, as you suggest.
Feel free to correct me though, more knowledgeable people.