The things very likely work so:
You have, for every draw you do, something like 2% chance to get a random rare and 1/1000 to get a random super rare.
In addition to this you have two counters, one for rares and one for super rares to normalize bad luck.
The counter for a rare in kage is 60.
To meet that 60 both draw by ten, single draws and free draws matter.
The same is for super rares, just that the counter is at 900 and isn't linked in any way to the common rare counter.
What happens if you are hyper unlucky and you never get a common rare before the counter gets reached?
You get one different rare after another without dupes until you got all of them and, at that point, you begin with a new streak of rares.
What happens if you get a 'lucky' rare in a single draw (Could be one of the ten in draw by ten, beware)?
Your current counter gets reset and so also your current streak of rares.
So, lets say you used 180 draws and got bee, mifune, danzo. If you didn't get any lucky draws in your 181-239th draw then your 240th draw won't be neither bee, mifune or danzo and you'll get your 4th different one. If you get a random lucky roll lets say at your 212th draw (that could be itself a dupe), then your counter resets and if you don't get lucky again you'll get your first pull from the new streak of rares at the 272th, this one could be again a dupe, because is a full new streak of rares (is more or less like if it was your first draw in the treasure), but if you don't get a lucky roll you can be sure 332th, 392th and so on won't be the same rares as 272th.
Now, the super rare counter works in the same way.
People that got the luck of the devil can get their first super rare as a random roll in theirs 1-899th draw, but if they do they can get a dupe when the following streak is met, while people that aren't lucky will get their first at 900 and at 1800 they surely get the other one (unless a lucky roll reset the counter by giving them a dupe in one of the rolls between 901 and 1799).
So, why people claims to get their first super rare after that magical 900 pull i said?
Because they base their calculation on the number of common rares they got before, giving to them the value of 60 each one.
But lets say they got very lucky and got every single rare at their 50th draw. Once they meet the 900 counter they picked up 17 rares before their first super rare and so they believe they used 1080 scrolls/free draws when, instead, they just used 900.