All three that you cite are different:
An SEP rating requires revalidation every 24 months by experience (12 hours + a flight with an instructor) or a proficiency check.
An MEP rating (or other type rating) requires revalidation every 12 months by proficiency check.
An IMC rating requires revalidation every 25 months (IIRC) by proficiency check.
An IR requires revalidation every 12 months by proficiency check (which can be combined with the SEP or MEP).
A night qualification is perpetual, but 1 night take-off and landing in the last 90 days is required to carry pax.