Most of that info comes from various videos and users personal experience. There are a lot of YT videos with 210 for jinch, 400 tendo or even some with ~3k pulls for ssn itachi, where you can see how often super rares occur. Some treasures require less seals, and a lot of people draw from them, ie. jinchuriki treasures which reguire 210~ draws for super rare to appear. When pulling from tendo was a thing, it was 400 for hashi/tendo. Kage treasure, like Danzo said. Now it varies from person to person, depending on personal luck. I've pulled mine at 841, groupmate pulled 3x 300 rebate and got it a while after that, so 900+, some people here on forum reported 1000+. Seems like in this 'big' treasure super rare appears usually after a certain ammount of pulls. Not neccessarily 800th, 900th, Xth pull is guaranteed SR, it's more about average range. Some mod (sorry can't remember name) posted on forum, that in theory you could pull super rare even with 1st pull, but odds of that are abysmal.

The only exception from the rule was after 3.0 was implemented, and kage treasure went nuts- most of the people I know who pulled SR before 3.0, got another SR in free draws without spending much scrolls- now it can be called whatever who likes, but it was simply too many people meeting certain criteria for that to be "accidental lucky pull", that happens less often than winning national lottery. But don't consider that, that doesn't seem to be the case anymore.