I can't find the original post even though I went through 10 screen pages of old posts. The question essentially was, 'How to use the PCGS submission form if you have more than 20 submissions at the same level.' It took this long for PCGS to respond. Just an FYI. "No problem, just on the submission form write "1 of 2" , and then "2 of 2" on the next submission form! You can have the submission have as many as you want when you do it this way"
There is actually an unset limit. PCGS called me when I did a 72 page, 1700+ coin submission. They said that while there is no official limit, they want the graders to be able to finish an invoice in one day.