Like many people, I experienced the odd phenomenon that iTunes would randomly not match one or two songs in an album that was otherwise matched. This seemed to be usually be a problem with matching, not a problem with the track source or encoding. This is annoying because it means that other devices that use iTunes match will have inconsistent formats. Luckily, with a little playing around I was able to fix most of these so that they match.
The most common problem seems to be that iTunes is overly picky about the exact length of the track (unlike most music-ID systems, that are more trusting of the acoustic fingerprints). A few seconds off and iTunes will no longer match a song. But by looking on iTunes to see what length it expects, you can then trim the song or pad it with extra silence at the end. This trimming or padding can even be done without re-encoding the track by using a program like mp3 Frame Editor (on Windows). There are other programs that either let you trim OR add silence, but I have yet to find another good program for doing both without re-encoding the file.
A few times I had to change the length of the file to something a few seconds away from the length listed on iTunes, so if you care about that one song that would complete the album, it's worth carefully trying several different lengths. The fastest way to do this, I've found, is to keep the original file in the iTunes library, then add a second copy with a different length (being sure to show the Date Added column to keep them separate) and then right clicking on the new file and selecting Add to iCloud. If it says "Uploading remaining songs and artwork...", cancel the upload, delete the file (telling it to remove it from iTunes match) and try again.
Despite my success with this trick, I still have a couple dozen tracks that I haven't been able to fix, so if anyone comes up with some other techniques, I'd be interested in hearing them.
The most common problem seems to be that iTunes is overly picky about the exact length of the track (unlike most music-ID systems, that are more trusting of the acoustic fingerprints). A few seconds off and iTunes will no longer match a song. But by looking on iTunes to see what length it expects, you can then trim the song or pad it with extra silence at the end. This trimming or padding can even be done without re-encoding the track by using a program like mp3 Frame Editor (on Windows). There are other programs that either let you trim OR add silence, but I have yet to find another good program for doing both without re-encoding the file.
A few times I had to change the length of the file to something a few seconds away from the length listed on iTunes, so if you care about that one song that would complete the album, it's worth carefully trying several different lengths. The fastest way to do this, I've found, is to keep the original file in the iTunes library, then add a second copy with a different length (being sure to show the Date Added column to keep them separate) and then right clicking on the new file and selecting Add to iCloud. If it says "Uploading remaining songs and artwork...", cancel the upload, delete the file (telling it to remove it from iTunes match) and try again.
Despite my success with this trick, I still have a couple dozen tracks that I haven't been able to fix, so if anyone comes up with some other techniques, I'd be interested in hearing them.