MP3tag is so flexible - it allows the user to customize the view so that you get the best information.
But you have to do the customization yourself.
So if you see differences between the tag panel and the file list, it would be up to you to synchronize them
The only exception is probably: you don't see pictures in the file list and you don't see technical information in the tag panel.
I strongly recommend that you get acquainted with the features as described in the documentation as you have asked a lot of questions concerning basic functions.
For this particular topic I would think this section is quite nice:
The list itself that pops up is not limited to those items. If you have custom tags, these can be added to either the tag panel or the file list. The exception being that the technical tags (those that have a leading underscore like %_filename_ext% or %_samplerate% for example) are not available in the tag panel, as these are not editable tags. For any tag field that you want to add that isn't in the current drop-down list, you can simply type it in to add it. This is especially useful for user-generated custom tags.