I think HTTrack is following links of start page 
Other links may appear external to HTTrack

 Try "all sites in page (multiple Mirror)": 
   Put URLs in Project Web Addresses list: 
     include URLs that link to 20-29, 30-39 etc. 
     so you should have about 10 URLs here  

You could also alter filters to be more inclusive
  but without seeing the page, I'm not certain how