So as far as I could tell, the answer is yes because it seemed to be what fixed my problem.
I was fast beginning to despair trying to relink a very short and simple sequence constructed partly, but not entirely of proxy media derived from 4K camera originals.
I was SURE I had done everything right. I had closed all bins except the one with the sequence and one with AMA linked camera originals. My proxies had identical names to the originals and also had been generated using Resolve in such a manner that the tape name was equal to the file name. I'd also successfully done a relink to the same batch of camera original media for another similar scene in the same episode of the program so I was quite sure I was doing the right thing.
Again and again and again and AGAIN I tried relinking to selected clips in ALL open bins with 100 different variations of parameters including the one that had worked previously where I told it to match original timecode by 'start' and source name by 'name'. Every single time no clips were relinked. Admittedly the sequence was simple enough I could have just manually placed the AMA clips in by matching the timecodes myself but I've had issues like this one before and frankly it's driving me CRAZY because I know it should work.
Eventually though I did make it work by pursuing a certain theory, but it just seems to me that my theory must be wrong even if the outcome was correct because it just seems unlikely especially as I can find no mention of it anywhere.
The proxy clips used to edit the sequence initially were sunc to external sound files via autosync which generated synced subclips of those proxy clips. Out of desperation I hazarded a guess maybe Avid just doesn't like trying to relink subclips. I was aware that manually replacing each and every subclip with its master clip counterpart was just as bad as manually putting an AMA clip over it in the timeline but I found instructions for automatically linking all subclips back to master clips here https://forums.creativecow.net/docs/forums/post.php?forumid=45&postid=87620... and so did that and then followed the same steps I had before, with my AMA linked clips bin open and my new master clip only sequence selected and then relinked the sequence setting the relink options Timecode to 'start' and Source name to 'name' and voila suddenly it worked.
Seems weird though. I don't remember well enough but I feel like the previous successfully re-linked sequences from the same episode in identical circumstances that just worked without all the extra hassle most likely would have used synced subclips too so my theory just doesn't sit right even though it seems to have worked.
I'll have to try some tests, but there may be a limitation lining to .sync clips? Or as you say, subclips in general. It may be that relinking to selected is to master clips only which in your case of double system audio would be two passes; 1 for picture, 1 for sound.