The pages feel thinner and you can see the text on the other side more as well. Book 6 is a 10th printing and book 7 is a 5th printing. Doesn’t say years, so I wonder if they switched to thinner or back to thicker?
I hadn’t noticed anything like that, but I did look at my book 8 which is 200 pages shorter than 7 and it’s the same thickness, so that has the thicker pages like 6.