OK guys we can digress down this road... but there is
AFAIK no known case of instrument training done outside the USA (in a European reg plane) being
disallowed for the award of an FAA IR, by the FAA examiner, on the basis that the instructor had an IMCR and not the full valid IR.
Well........... except as part of a blatent revenue generating scheme as run by certain UK based FAA flight training establishments in years gone by, but the FAA DPE was not involved in the refusal. I did my FAA PPL in the UK, and then spent much of 2004 trying to do the FAA IR in the UK too, in my own plane, only to find that not only was nobody able to guarantee the availability of the FAA (visiting) examiner, but also some of the merchants came out with utter tosh like "all training towards an FAA IR must be done by an FAA CFII" which "everybody" would recognise as utter crap but it was a case of quietly saying "sod it", getting one's credit card out, and doing 15hrs of flying. In the end, the examiner availability problems (which resulted in legal action by some candidates to get checkride deposits refunded) were enough and I went to the USA.
I have it in writing from the FAA that they regard the UK IMCR as equivalent to the FAA IR - within the respective legal privileges of the two ratings obviously.
My own experience is that various FAA CFII instructors hold the UK IMCR in high regard.