Installing tile on stairs

I am sure this topic is all over this forum, and if someone wants to redirect me to a thread, please do, but I am trying to get a better sense of acceptable lippage on a 12 x 12 porcelain tile. I have laid about 90 sq feet and have about 40 to go. When I test the lippage variance using the quarter test - or as I understand the test for lippage, the width of a quarter between corners (.066") I have several corners that exceed that amount (though not by much) and 2 corners that are closer to 1/8, though in a closet. Over the total, I have about 8 corners that are not with the variance. BTW, some people recommend a credit card thickness, but that is much less that the quarter thickness (or the .066" that I have read as the ANSI spec) I am using 1/8' grout lines. My question is: how bad of a job is this? If you were laying tile in your own home, would you think you had a made of mess of this or that it was okay? It looks okay to me, though I haven't grouted, but a couple of spots catch a toe. I laid this in the basement of a raised ranch. I laid this over a 1/2' hardibacker, over a 3/4" T&G subfloor, floated and anchored over 1" XPS. Some people thought this would not be an acceptable subfloor for tiling; maybe I am finding out why this wasn't a good subfloor or maybe I am not a good tiler or maybe these are acceptable variances. But the subflooring was hard to get level - I guess I should have used a leveling compound. Anyway, any thoughts from experienced folks?

I've currently got ceramic floor tile on cement board on wood. I want new tile (some ******* decided to save $ with cheap tile with blemishes everyhwere). Am I correct that I will need to remove and replace the backer board? I doubt that I could just split off the tile and thinset. I'm also pretty sure that I wouldn't want to plan on reusing the backer board. My questions: 1. Am I correct that I will need to remove and replace the backer board? 2. How do I go about removing it? I see videos of people using a mini-circular saw to cur out each individual tile and pop them out one at a time. I think that will only work well if there isn't thinset btw the board and the substrate. 3. What if there is thinset btw the backer board and the wood floor? Is this a good time to poor the back board? I've only placed new tile over new backer board on original substrate.