Rove!
Footballguy
If the sequel or prequel is generally as canon by creators or fans and changes and/or retcons the canon of the good films in the series, then yes, it can ruin the original works.None.
I dont understand how a movie that came out after another can ruin the first one. You can still always go back and watch the greatness of the first one. Godfather 3 didnt make 1 or 2 any worse. The upcoming Ghostbusters will not ruin the greatness of the original. etc. etc.