The releases do not really have catalog numbers. For M4 to M7 the releases were numbered in their titles, so the catalog numbers are assigned after these titles (as can easily be seen below). The first three releases have their 'catalog numbers' assigned in order of appearance. The original EFA release of the CD didn't feature any catalog number besides the distributor's, as well, 'M-CD' is only given to fit it in with the rest.
Official catalog numbers can be found on the labels homepage.