Hi
It can depend on the airline, they may want the IR to be current, however, assuming you are being type rated on a multi crew aircraft then it isn't actually a requirement.
By the end of the type rating you will have a Multi Crew IR, but you can't then jump into a Seneca and fly airways. You will need to revalidate your Single Pilot Multi-Engine IR to do this.
Best of luck with the type rating!
Le-Slat