So looking at CAP 804 Section 4 part H it states the following:"have passed the ATPL(A) theoretical knowledge examinations in accordance with this Part; and..."
Since it states "in accordance with this part" I went through the rest of CAP 804 regarding theoretical knowledge, mainly part 1 but also Section 4, Part A, paragraph 3 that also refers to Part-FCL.025 (c)(2)
After looking through that lot there isn't anything to challenge the statement that you merely need to have "passed" the ATPL theoretical knowledge at some point, there is however this little gem in FCL.035 "Crediting of flight time and theoretical knowledge:"
"(5) Notwithstanding point (b)(3), the holder of an IR(A) who has completed a competency-based modular IR(A) course or the holder of an EIR shall only be credited in full towards the requirements for theoretical knowledge instruction and examination for an IR in another category of aircraft when also having passed the theoretical knowledge instruction and examination for the IFR part of the course required in accordance with
FCL.720.A.(b)(2)(i)."
So I get that's to stop anyone doing the CB-IR and using that theory to claim IR theoretical compliance for a multi crew type however it does state that you can actually do that if you have already "passed" the IFR part of theory examinations with no mention of time limit.
FCL.720.A.(b)(2)(i). merely loops back to the original statement of:"(3) have passed the ATPL(A) theoretical knowledge examinations in accordance with this Part; and..."
So in theory, it looks like you can actually add a multi crew type with expired ATPL theory as long as you have "passed" all the exams at some point, you certainly cant use them for issue of a CPL or IR or also to then upgrade to a full ATPL which would mean you are stuck forever as an FO on a multicrew type!
I spend a lot of time reviewing industry / contract law in my day job and it never fails to amaze me what a mess of vagueness the CAA / EASA documents are....!
Regards
UA