That's not what is written though is it? ATPL exams are downward creditable, and the time limit depends on what you want to use them for: PPL 24 months, CPL and IR 36 months etc. It stands to reason that you can't use them for an IR after 36 months, true. But where does it say that if you don't use them for CPL and IR issue they are rendered invalid for ATPL purposes? That's more of an inference than a fact. I see no reason why separate IR exams wouldn't work - the OP would hold a legitimate CPL/IR - so only the 7 year rule would be relevant.