Interesting theories - m6 ceto rather than M6CSL... maybe m is for Michael.... haha.
I'm thinking it would be to do with the test model version ie ceto 6 design test version M. It would be an easy way identify the various iterations (you get 26 options) to do computer aided analysis. You would hope that they wouldn't get to version Z. then each version would have M.A, M.B, M.C etc. until it was accepted as the construction version ie M.0 .
Alternatively it could just be a simple revision of the one model but it is rare to get to an m Revision unless the design was really old. only the ASHKAN would know..... someone hit him up on linkedin and ask.... hehe.
depending on the differences in test versions they could potentially be turned into future ceto models ie 7 8 9 X etc...
