The number of tickets should fixed based on the published odds and winners for that game.
Take your Red Hot 7's game for instance, you can tell by the top prize odds how many tickets they have. Odds 1 in 1,200,000 and 20 top prizes available = 24,000,000 total tickets for that game.
I've never seen any scratcher tickets with book numbers starting below 100000, so with 80 tickets per book for a $5 game, you should see book numbers from 100000 to 399999.(tickets 000-079 for each book)
I liked Red Hot 7's, nice easy game and good odds. Was playing that game heavily for a while until I switched to Wild 10's. They seem to be selling very well too since it looks like they did a re-order on that game. Initially when the game came out it was 17 top prizes, or about 20.4 million tickets:
But then looks like it was a hot seller for they ordered 3.6 million more tickets, added 3 more top prizes: