get this, Schwalbe Supreme tire in 622 diameters is called a 700c when it's 32-40(622)size, but it's a 29x2.00 tire when it's 50-622 size,,which is pretty crazy since it's the same diameter rim. Head over to the Dureme model and the 50-622 tire is called a 28x2.00. So the same size 50-622 size tire gets called a 28" or 29" tire. BUT if you get a 50-622 XR it's called...a 700x50c.
So there you go, one manufacturer with three different designations for tire diameter for the same damn size rim. 700c, 28 or 29!!
http://www.schwalbetires.com/marathon_supreme
http://www.schwalbetires.com/marathon_dureme