Are they the 5E versions? It's different to what the website says.Looking at my copy
Book 6 9-11
book 7 11-13 (You get teh 13th level just after the end of the adcventure and before book 8)
Book 8 13-15 ,again 15 is at the end of the adventure
Book 9 15-17 finishing at 17
Book 10 and 11 takes you to 20
then book 12 and 13 have no levelling. So you actually get to play level 20 characters for more than one combat scene as is more common
So the progressionis pretty much the same for books 6-9 and slows a bit for 10-11
I was looking at the Gears of Revolution AP on the Zeitgeist website and I was a bit confused about the adventure levels.
edit -- 5th edition version
#5 level 7
#6 level 9
#7 level 10
#8 level 13
That's a big jump from 10-13. Is #7 especially long?