Greenwings,
A current single pilot IR is only needed for issue of your first multi crew type rating. Now you have a Multi crew Rating on your license you may now add another multi crew type (JAR25) with out holding a current IR.
So if you were offered a job on another JAR/CS 25 type then regulation wise there is no requirement for you to have the SPA or MPA ME current (as Sky Captain has stated).
Greenwings when you join an operator they will need to do an OCC (operational conversion course) where you will do an OPC anyway which can be used to revalidate your rating (now it is down to the company if they will accept you without the rating current).
Now you do raise a good question concerning the JAR23/ Single Pilot types, now King Airs , Beech 1900s although often operated multi crew are only single pilot class / type ratings.
Now I couldn't find an answer in Lasors. So with a lapsed SPA ME IR but and a MPA type non current (but expired less than 5 years) you can definately still undertake another MPA type, but it isn't clear if you can still then add a single pilot class/type rating without renewing the SPA MEIR first.
Now for the five and seven year rules it doesn't matter which IR has been renewed aslong as you have renewed an IR in that time.