Tags, "Names", Fields, etc. cross-reference

I've been spending a huge amount of time trying to match up Tags, Names, Fields, Placeholders, Frame Names, etc., etc. in MP3Tag, Exact Audio Copy, and other programs that I sometimes use. Mp3tag Help - Tag field mappings and Tag Mapping - Hydrogenaudio Knowledgebase are helpful, but I haven't yet found a comprehensive cross-reference of all such "names" for EAC and MP3Tag, so I'm having to build one myself in a spreadsheet. For example, MP3Tag seems to use ALBUMARTIST as a tag, but I haven't yet found a reference to whether there is a %albumartist% placeholder in MP3Tag, as there is in EAC. In addition to answering that specific question, can anyone point me to a comprehensive cross-reference of tag names, placeholders, and ID3v2.x frame names at least in MP3Tag? Thanks.

As you already looked at the help the tag field mappings, the columns that you have to compare is the one with the heading " ID3v2.3"
The 4-Letter-Names represent the tag field names as laid down in the id3 standard.
In EAC you have to look at a similar list and align the matching ones.
As MP3tag writes information to files with different tag standards, e.g. ID3 TPE2 is addressed as ALBUMARTIST in Mp3tag - and aArt in mp4 files also maps to ALBUMARTIST.
So I would think that the information is already there.

Thanks for the reply. The tag field mappings page has a columns called "Name in Mp3tag" and "ID3v2.3". However, as I understand it, placeholders are different and may or may not exist and may or may not use the exact same name as the tag. Is that correct? If so, is there a complete cross-reference of MP3Tag "names", placeholders, and ID3v2.3 tag names (when applicable)? If I had that, I should be able to build the cross-reference to EAC and other applications. Thanks.

The variable names to access a certain piece of information are described on the mentioned help page.
You only use these variable names.
If you are not sure which piece of information ends up in which variable, then check the extended tags dialogue (alt-T). There you see the variable name and the stored information. So if you enter information in another program (and that stores it in the tags) then you will see how to access that in MP3tag.

Perhaps some definitions: a tag is the whole information that is stored at the beginning or the end of a file. That tag is then structured into fields, atoms, chunks, vorbis comments - but that depends on the tag standard and file type.
In Mp3tag you don't have to bother which structure has to be served, where the tag is saved - this is done by MP3tag.