Last post was made in a hurry before heading off for a few days. Hence the delay.
That other thread is incomplete. I was waiting for a comment from Dana that never came. A number of other posters offered comment, but as their problems were different to mine the thread got a bit confused.
In the end I gave up and put a piezoflush cart in that slot. I had been using the printer for Piezography K7 and so the yellow slot held shade 7 - the lightest shade with the least pigment - without any problems. I switched from K7 to P2 (which uses six shades rather than seven, which allows you to put photo shade 1 in the Y slot where shade 7 used to go, which removes the need to swap photo shade 1 and matte shade 1, i.e. MK & PK). The problems started shortly afterwards.
All my attempts to clear it were successful for only a short time. Eventually I tired of this and put in a flush cart which has stayed there ever since. This worked for me because I mostly print on matte papers - I use the Special Edition inkset and find it too warm on PK papers - and so it hasn’t been a major problem to leave flush in that position. I have it in mind try again in the near future, although I’m undecided whether I should try photo shade 1 or shade 7 again.
In terms of using the cleaning kit with the syringe, it’s two years ago now and I don’t recall. I suspect not, as I probably thought that there was little point if a purge pattern cleared the problem, albeit briefly. But it’s all academic now, as for the past two years I’ve always had a perfect flush nozzle check. Hence why I considered having another go with ink in that slot.
In your case … who knows? I’d like to think that I’ve got to the bottom of most printer problems that I’ve encountered, even those I didn’t resolve. But not that one. It remains a mystery.
I think most of your guesses about abbreviations are correct. The other purge patterns - the ordinary JPGs with coloured columns - will sort of work for purging. But they won’t give you pure prints from each channel. They’re in RGB mode and the printer driver converts them to a CMYK colour space, and if you open one of those purge JPGs and convert to CMYK you’ll see that every column becomes a mix of C & M & Y & K, even the pure Yellow bar isn’t just Y. Mostly Y, and probably enough for purging, but not 100% Y. Ditto for M & C etc. Just remember this. It’s why I prefer those special TIFFs and calibration mode.