The Isle of Cats contains 38 lesson cards. This includes 14 core lesson cards and 24 lesson module cards. Additional lesson module cards are available in expansions, if you ever get more, then follow these rules.
Core Lesson Cards
You must always use the 14 core lesson cards included with the game. These can be identified by the text on the bottom left corner of the card that says "LESSON" and nothing else.
Module Lesson Cards
You must always use exactly 3 complete lesson modules. These can be identified by the text on the bottom left corner of the card that says "LESSON" or "PUBLIC LESSON", followed by a letter in brackets.
Each lesson module contains exactly 8 cards. Included with the game you have lesson modules A, B, and C. If you get a new module you can switch it with any existing module, but you must always swap all 8 cards.
You can mix and match lesson modules however you wish. You could use modules A, B, and D, or you can use D, F, and H.
Oshax and Rare Treasure Promos
There are several Oshax and rare treasure promo tiles available for The Isle of Cats. If you ever get one, then follow these rules.
New Oshax tiles should be added to the discovery bag. These work in a similar way to rare treasures.
When drawing tiles from the discovery bag, any Oshax tiles you discover should be added to the other Oshax tiles you have available.
Oshax tiles do not count towards the total number of cat tiles drawn from the discovery bag.
When you finish playing, you may choose which 6 Oshax tiles to keep out for your next play of the game and return the remaining Oshax tiles to the discovery bag.
This way you will cycle through all of the Oshax tiles and start each game with a new combination of 6.
New rare treasure tiles should be added to the discovery bag. They follow all the normal rules for rare treasures.