Looks like I've already got the answer to my own question:
EDIT: Scratch this, found out that those who bought higher tiers before don't have to wait to catch up per se, because 30 chapters have been mass released to the normal readers for these novels. So it's all good! ✌
It looks like the novels that had offered higher tiers than 20 advance chapters before, have now set their max tier at 20. This means that readers, who had bought higher than 20 tiers of privilege for these novels before, have no other option but wait, because even if they decided to extend their privilege access by buying the current max. tier of 20 advance chapters, they'll still have to wait until the chapters difference between the latest chapter of the 20 tier, and the chapter where they were at before when they bought the higher than 20 tier, is reduced to 0.
It's fine, I'm not complaining, it's good that you adjusted the program as per the users feedback, but I think you stil should communicate better with your customers. As I said before, this forum post is inadequate as not everyone is a forum-goer. I wouldn't be surprised if there was another wave of complaints from a bunch of confused privileged readers out there that don't know anything about this adjustment, and will then, again, think that they've been cheated by you guys. Good luck with that.