1) The data retrieved by RMTV depends on what the data provider has available - I have no control over this unfortunately;

  - sometimes new seasons take a bit before they become available
  - some providers are quicker than others (try selecting TMDB instead of TVDB for example)

2) Some series have a different numbering depending on it source, eg. Aired vs DVD. But also: Netflix notoriously changes episode order and sometimes even season length

  - Check the episode naming (if available) to see if episode naming matches with your filenames (eg. Title)
  - Netflix sometimes changes the order, splits episodes or merges episodes etc.

3) Some episodes in a given season reside in the "Specials" - in this case it could be S00E02 or S00E03 (link)

Looking at "CSI: Crime Scene Investigation (2000)" (I couldn't find your title), TVDB, TMDB and TVMaze indeed shows 17 episodes for Season 8 (as you can see on the TVDB page as well - link). Note that even IMDB lists only 17 episodes for season 8 (link).

So I honestly would not have a clue where the missing 18th episode would be or if there should even be such an episode.