Quality of play-back of videos saved as movies in movie maker

I created a video/slide show with music in Movie Maker and saved it as a movie in Movie Maker in HD.  It was fine and played back pictures and music sharp enough on tv screen and computer.  I wanted to add a couple frames to the end so I went back to Movie Maker and imported the saved movie and added a couple more pictures and movie and re-saved the new version as an HD movie.  This movie version is noticeably fuzzier than the original.  Since I don't have the .wimp version anymore, importing the original movie was the only way I could see too add to it.  Should I expect saving a movie from the original movie would degrade the quality of the same movie?  It also skipped in the play back.