Skaz As I said, why are you claiming that 81 should be unlocked, when I already explained that it's literally impossible to unlock them? You are just under the impression you unlocked them because you could read them. And if you start a book long after, there's obviously a lot of free chapters you did not unlock.
Premium and ads are different also. A lot of books from that era went through
1. Completely free
2. The latest 2-4 chapters are locked by ads (first instance of doing an actual transaction)
3. Full premium for new chapters (still unable to actually 'unlock' old chapters that are free to read because there's no mechanism to do a transaction)
4. Retroactive locking of chapters to somewhere around Chapter 100 (varies based on book)
Suppose the book is consistently releasing 1 chapter a day.
1. Book has released to Chapter 300 for free.
2. Book enters adwall system where only the latest 2 chapters are locked. Chapter 301 and 302 onwards are available by ad unlocks. Someone chooses to let the chapters stockpile instead of watching ads/using SS to unlock them as they get released. After 7 days, Chapter 301-307 are free to read. Chapters 308 and 309 are locked. You start following the daily release, so you unlocked 308 and 309, and subsequent 310... Now, if you did that, you lost the ability to make a transaction for 301 to 307, since they were released free to you.
3. Book goes Premium at Chapter 400. You continue unlocking from 400.
4. Book gets retroactively relocked to Chapter 100. Chapters 101-300 are now locked, since you never had a chance to unlock them prior to stage 2. 301-307 are also locked, because you chose to stockpile free chapters. But 308 onwards should be unlocked, unless back then, you chose to stockpile post-308 chapters randomly or just didn't have time to follow the release on a daily basis.
You sound like you joined in stage 3. But all those chapters before the Full Premium were not unlocked. Now that the book enters stage 4, you start seeing a lot of chapters that are locked, because you just didn't have a chance to unlock them while they were being released under stage 2.
You definitely bumped into chapters that needed unlocking. Are those unlocked? But what about the initial chapters you read? You obviously did not pay from Chapter 1. Then, if your memory is good, can you say which chapter was the one when you first actually started unlocking? I'm guessing it's 341 for Trafford's Trading Club. It should coincide with the period when you actually started reading this book and finally caught up to the release. If you can be honest about that, we can continue figuring out if there're any problems.
Up to now, all the cases seen have been the same. And I haven't seen anyone provided enough evidence otherwise.
This is something that memory can easily fail you, because unless you can swear that you were a religious reader who reads a chapter the second it is released, it's very likely a few days of break, simply because of the very understandable reason of stockpiling or being busy with real life, you can have holes in your chapter unlocks.
The reason why everyone seems to have different numbers is dependent on when they actually started reading, or when they started doing an actual 'transaction'. But that's exactly what the system is supposed to do. You made a transaction, the chapter is unlocked for you. You read the chapter free, when the retroactive locks happen, those chapters are locked.