The 13s 15’s and 17s figure into the sequence of serial numbers too. Our 21 was built in the fall of 2013 and was the 766th Escape built. Since there was a block of Escapes built and sold as an introductory release and we have met and talked to several other owners whose Escapes were part of this “offering” we know ours was the 6th 21 built and sold. I had a nice conversation with Reace on this at the Escape rally in May of 2019. Along with comparing numbers with a couple other owners who were at the rally i feel confident on our “vintage sequence”. We know numbers 3,5,6,7 on the 21s. In addition there were three 21 “prototypes” according to Reace, not figuring into our calculation of sequence. Wish I could help you more. Just understand that the serial numbers are not “specific” to a particular model but to the overall builds.
Iowa Dave