Originally I think that was the case. But, exit numbers have been used on state highways since before we transferred over to this site. A few examples include M-53 and M-14 in Michigan and SR2, SR11, and SR315 in Ohio. I don't think we've gone back and changed much along the way, but there is precedent. I can't think of a US highway that has included them yet, but I know it was talked about.