(b), a further differences training or a proficiency check in that variant shall be completed, except for types or variants within the SEP and TMG class ratings.
I don't read that to mean that that the differences training on MEPL is not valid for SEPL (or TMG) as you say. Read; "except for.......": i.e. the differences training on a MEPL is valid for SEPL but not valid on other MEPL.