The problem is that I can't easily see which tag is on which track (and what is the value), without manually adding a column for each one...
Would it be possible to add a small "add column" in front of each tag of this list, which would create the corresponding column? (or even better, a "add a column for every tag which do not already has its column" button )
Before I would add that many columns, I would join those with different spelling but probably the same contents, e.g. TIME_REFERENCE and TIMEREFENCE or PURCHASE DATE and PURCHASEDATE or UNSYNCED LYRICS and UNSYNCEDLYRICS.
And I would then make a list of fields that I really want to keep.
Also, I would see which tag versions are summarized like that. An indicator for me is that TOTALDISCS and TOTALTRACKS are no fields for mp3 files as this is data is saved in DISCNUMBER and TRACK. So I would assume that you get a lot of blank columns which should be blank as these fields serve not purpose for that file format or are the product of a rather individual approach to name the fields.
Yes, the idea after that is to see which tag is relevant, which one I want to keep, and to drop all useless (for me) tags, but only after I'm sure I don't drop any important info.
I think it is just as quick to filter for files with strange fields with
%strangefield% PRESENT
If I look at the enormous length of the extended tags dialogue, you would have to do a lot of scrolling and sorting to find the fields that have a contents. And then, to delete them, you would have to open the extended tags dialogue anyway ...
But the future will show us what will happen to this idea.