Searching API By ISBN does not give up to 40 results

[Vishnu]

I am using the Goodreads API with my website to show the average review for each book for a list of (up to) 40 books. When I try to get the reviews by ISBN (isbns=1,2,3,4 for example), Goodreads does not give me 40 results, usually stopping at 33. I tried the same search but with 30 books, and it gave me only 24 results. Why is this happening, and how can I fix it?