That hidden value .. seems like hoax cause it doesnt make any sense otherwise it would have been known and everyone would pull on such specific day of the week where he/she can get the ninja they want.

Anyway about my experience. I have already pulled super rare 'Ay' after 870 seals. While i got many duplicated during the journey to super rare; i still never pulled Mei for once xD and yes never gonna spend coupons for her. Since i stopped pulling from kage treasure so you can say that i will never have her unless they will be free in future events :P

anyway, the whole concept about treasure its complete RNG with some prediction about the number of pulls that can get you a rare. So good luck with your next rare hopefully you will get what you want.