How to show the values of the "minor" ID3 header?

The column "Tag" shows the presence of the various ID3 headers in a song

So "ID3v2.3 (ID3v1 ID3v2.3) says both ID3 headers are available.
But in the other columns always the values of the "higher" ID3 tag is shown (here ID3v2.3).

How can I peek into the values of the "lower/minor" ID3 header (here ID3v1)?
...or even change/edit it manually?

In Options > Tags > Mpeg you can choose whether ID3v1 / ID3v2 should get written to files and which ID3v2 version to use (2.3, 2.4).

Not sure what you want to achieve in the end, though.

You have to set Tools>Options>Tags>Mpeg
to read only V1 tags and ignore all others.
It may be an idea to export the V1 data to a text file.
Then set the options to read only V2 tags.
Export also that data to another text file, then compare the data.
You may find that V1 data is concatenated in comparison to V2 data.
Also, you will find that V2 data will have more fields than V1.