Is there not also a requirement that the certificate of renewal/revalidation (whatever it is called) also be signed off at the time of the test?
So if you did your MEP and ME-IR renewal tests you should have the SEP certificate signed at the same time?
No you only have to provide evidence to the examiner issuing the CofR by experience for SEP that you've carried out a skill or proficiency test for a UK licence/rating within the 12 months preceding the expiry of the SEP rating. The signed up card should be sufficient.
However, if your SEP/MEP ratings aren't in synch and you have the hours in the second year by the time you do the MEP test, there's no reason why the examiner shouldn't also revalidate your SEP rating (valid for 24 months from expiry) as you've then met all the requirements.
Now can you find the reference that allows an IMC rating to be renewed at the same time as an ME-SP-IR renewal in a sim.
Unfortunately I can't. The stuff in LASORS E 3.4 which covers that sort of thing is delightfully contorted. I've always done a test in an aeroplane for IR renewal and the examiner has always also signed up my IMC rating on request.