Quality of playback with videos saved as movies on movie maker

I created a slideshow/video in Movie Maker and saved it as an .wmv  HD  movie in Movie Maker .  The playback was fine on both TV and computer.  I wanted to add something to the end of the movie, so I imported the movie into Movie Maker since I no longer had the .wimp version.  I then added some pictures and saved it again in the same way.  On playback, however, it appeared fuzzier than the original.  Should I expect that using the original movie rather than the original pictures would result in a degraded finished product?