I appreciate this reply comes some time after the OP's post about the fare but thought it would be helpful to share my experience with this as a data point.

Having initially looked into this using ITA Matrix and dismissing it as likely unable to be ticketed in mid-2024 (after the OTAs Powertools linked to failed to generate anything bookable), I looked again in January as I was planning a trip to Japan this year with my mum for a big birthday. By that point, I'd accrued 600TP so the prospect of being able to secure BAC Gold again before the end of BAEC was tempting and I found a MAD-AMM-BKK-HND return fare for ~£1750pp (2 of us travelling) with outbound 12/03 and return 22/03 (based on both outbound and inbound being ticketed in D).

This time, I first tried calling both RJ and JL but neither could ticket it: RJ said they couldn't access JL's side and JL said something similar though they were more helpful and explained that they were unable to see any D availability on the RJ side). Because a few of the OTAs Powertools sent me to did generate something bookable, I then went down that route and ultimately was able to book with MartiGO.

I was apprehensive about using MartiGO based on Trustpilot reviews and a little more so when I received a WhatsApp advising that - despite having paid already - I would now need to pay another ~£150pp as they could only ticket the return leg in C. Thankfully, the agent provided a PNR reasonably quickly and the full itinerary (with both of our BAEC numbers correctly pulling through) came up on the RJ app. I used Avios for the Y flights to/from MAD on 08/03 and 24/03, factoring in a couple of nights in MAD on the outbound sector (as neither of us had been).

Discounting the 2 nights we had to sleep on planes - both of which were on RJ 787s - we ended up with 2 days and nights in MAD, 1 afternoon/night in BKK, 10 nights in Japan, and 1 day/night in AMM.

I'm conscious this is my first post so won't be able to post any screenshots/photos (and will be limited in the number of follow-ups I can make for a little while) but would be happy to share more if it'd be helpful.