Well you could intentionally turn your pool green by SLAM'ing it, and then keeping FC on the higher side for a couple days as you're filtering it out with the polyfill in your skimmers. After you get it out, you can lift the stains on the stairs with spot-AA treatments probably, and sequestering the stain.
I still think something odd is happening in your pool, and I can't put a finger on it, because when you've raised FC to 1-2 after an AA treatment your stains reappear and that's not typical at all, especially since you've been using Jack's purple as a sequestrant. Would you be able to share information on ALL the different stuff you've ADDED to your pool this season? (Yeah, I know that's a big ask.. sorry) Maybe there was some kind of magic potion added or something that is causing a reaction with something else. Also, just for kicks, have you tried Jack's Stain Identifier kit? I know you mentioned that AA does lift the stains on the stairs, so that points to iron, but, it might not hurt to try their Identifier kit to see if your staining reacts to anything else as well. I wish your other thread was getting more responses from TFP, but unfortunately, your issue is really, odd... ?