PC to iMac iTunes Switch. Several 'original file could not be found' errors

I am hoping someone can help me find a resolution to this issue that might save me a bunch of time.

When using iTunes on my PC I had "Keep iTunes Media folder organized" and "Copy files to iTunes Media folder when adding to library" both checked. And I consolidated the entire library again just to be sure.

On my new Mac I trashed everything in the iTunes folder, emptied the trash and copied the entire contents of my PC iTunes library into the Mac folder.

For the most part it worked -- the Mac sees my playlists and my entire library. But probably 20% of my 1900 song library has an exclamation mark and says "original file could not be found"

If I manually locate the song, it is sitting right there just where it should be, but I sure don't want to manually locate 400 songs.

Does anyone have any tips for what might have gone wrong and how I can resolve it?