About treasure chests

Hi
Is it true that there's only one rare item (xtal, skill book) in treasure chests on the maps that are from the same Main Quest chapter in one day?
For example if I got Maton Sword in Droma Square then there won't be any xtal or skill book in other Chapter 7 maps like Brahe Lab, Ultimea Palace, Monster Forest, etc in the same day
I got this information from some random dude in Hora who claimed he's treasure hunting for weeks

 

From my experience, nope. I've gotten two rare items -- one from Lufenas Mansion and another from Brahe Labs -- in a single treasure hunt run, and that entire run took place in the same day.

 

I see, thanks

 

Yeah. A friend of mine got 3 xtal in a single thunt run once and a few got 2 in a day.

 

I got 2 xtals back to back at monster's forest in a single treasure hunt before.

 

it's just random.
pull rates are hard coded, there's so invisible system involved that affects your chances of getting a certain item.
same for paid gacha, potum darts and box items.