track info missing after importing music library to new computer

I recently re-imported my music library to a new computer. Most songs imported correctly, but at least a third of them were placed in an "Unknown Artist" folder where the song titles all had leading track numbers (and therefore would not alphabetize correctly) and other track details (album, composer, genre, etc) was missing in iTunes. Yet when I looked at these files under Properties > Details the info was still there! This glitch only happened with tracks that had track numbers (many singles in my library have no track number, and these all imported correctly). The only thing I found that fixed the problem was to delete all track numbers in iTunes and also delete them from the "#" column in the Details. Yes, this was a royal time sink for me, but now my library always imports correctly with all track info intact. For most of my rock library I don't care about track number, but it does make a difference for concept albums (such as the Who's "Tommy") or for classical music with multiple movements. Since the problem doesn't occur consistently, it's worth trying track numbers for certain music. For classical music I incorporate movement numbers into the track names so that they always play in order. For example, "The Planets: 1. Mars", "The Planets: 2. Venus", etc. Music can also be imported from CD with the tracks merged to keep them in order, but this isn't an ideal solution either. Of course iTunes should just work properly and I shouldn't have to go to all this effort, right??