Update: I figured out pity and finally got Tiamat (learned what not to do on banners)
Follow up to my post from earlier this week about why I kept going past the number on the banner without getting Tiamat.
Some people explained it simply: the pity is for the featured 5 star on that banner and only counts actual summons on that banner, whether singles or 11-pulls. I had mixed in a bunch of tickets, kept switching between banners when I got tilted, and was tracking total SQ spent across the whole event instead of the actual summon count on the one banner. In short, I made the worst spreadsheet possible.
So I started over, tracked pulls properly, stuck to one banner, and stopped doing angry random singles. I also set a hard stop so I would not keep chasing once it started stressing me out. Result: I hit pity correctly and got Tiamat at the guaranteed point. Huge relief.
If you are new or just play casually like me, my takeaway is: do not panic pull and do not bounce between banners if you want to rely on pity. Write your pulls down in a simple note so you are not doing mental math at 1 AM.
Thanks to everyone who explained it without roasting me. Now I can go back to actually playing the event instead of staring at the summon screen.