For those with IOS devices or are simply using iTunes as your primary music manager, you will find that mp3tag is far more flexible and powerful than the built-in
Get Info editor. However any changes made outside of iTunes will not automatically be reflected into any music files that have already been loaded.
There are two ways to get these changes to be reflected into iTunes.
Get Infopanel for each track. This will force iTunes to grab the latest metadata info and overwrite whatever was in the library file. But this has to be done for each file that has been updated, and is not a simple solution if you have made changes to a large batch of songs.
Force the info from each file to be written back to iTunes. This can be done by using an external script program. Depending on how many tracks you have selected to be changed, this could take anywhere from a couple of seconds to several hours. So to cut down how long it takes to scan, try to only select the files in iTunes that actually need to be updated.
Examples of scripts that I have found useful online (for reference only, use at your own risk after checking for any security concerns);
Windows (thanks to Steve MacGuire): UpdateTagInfo
Mac (thanks to Doug Adams): Refresh a Track From Its File's Metadata
There are likely many others around, but I have found both of these to be useful in my case.