JAR-FCL 1.235(c) does apply to SEP - read it
OK then:
(c) Variants. If the variant has not been flown within a period of 2 years following the differences training, further differences training
or a proficiency check in that variant will be required except for types or variants within the SEP class rating.
It seems to me that that paragraph specifically excludes the SEP rating.
What's more, that paragraph does
not state that if you haven't flown a variant for two years, you will need to repeat differences training.