Anyway, for the purposes of getting an FI or MP TR - there are no validity periods mentioned
No, because these are ratings; the exams are required for licence issue as well as initial MP TR however the assumption that a type-rated first officer revalidates an IR through an LPC/OPC within the 12 months before expiry, means that the ATPL credits are refreshed. Similarly, an FI who revalidates an IR each year maintains exam credit 'currency' but there is no credit extension offered to an FI who has not renewed an IR for more than 7 years.
I've attempted to give some practical advice based on actual experience. From the perspective of obtaining an FAA IR to circumvent the 7 year rule, based on my understanding of the FAA IR, for someone looking to achieve a job flying EASA types in the EU, you could better prepare yourself by just renewing the IR in the EU in view of the fact that you will need to undertake the proficiency check there regardless. If you haven't used your ME IR for 7 years, best of luck to you getting through an assessment with an FAA IR and previous, distant experience.