Most Likely Bogus, But Interesting Regardless
R7b doesn’t exist. Best case scenario, this was done privately, not officially. Certainly the nature of the perforations indicates it was not done on a normal perforator. I thought it was interesting enough to put in a snipe and won it for a nominal bid.
It’s an early cancel, and during this period some companies were looking for ways to make imperfs easier to use. See, for example, the sewing machine perforations on R19a and the privately rouletted 1st issues (only a handful of examples reported).
Regardless, I found it a curious oddity.