Originally Posted by
BobbyItaparica
Only one set of extra pages (24 pages are in each set) can be added to your passport at a time, but if needed, and if your passport remains in good condition, you may have up to three sets of extra pages inserted into your passport.
Even the first part of that isn't all that consistent. The US Embassy in London put three sets of pages in at once since I had managed to fill my passport in just 4 months since new.