It's pretty self-explaining:
JAR–FCL 1.495 Acceptance period
(a) A pass in the theoretical knowledge
examinations given in accordance with JAR–FCL
1.490 will be accepted for the grant of the
CPL(A) or IR(A) during the 36 months from the
date of gaining a Pass in all the required
examination papers.
(b) Provided that an IR(A) is obtained in
accordance with (a) above, a pass in the
ATPL(A) theoretical knowledge examination will
remain valid for a period of 7 years from the last
validity date of the IR(A) entered in the CPL(A)
for the issuance of an ATPL(A).
So you have 7 years after the date your IR(A) (JAR doesn't care if it is single or multi-engine) has expired to complete all the requirements fo ATPL(A) - or simply just renew your IR(A) rating.