Embedding ISRC code to wav file

I have released some tunes on CDBaby, by sending my master files to them.
They assigned ISRC codes.
Now I need the files, with ISRC codes, to send to the US copyright office.
CD Baby does not let me download their version of the files, and recommended MP3tag as a way for me to embed the ISRC codes myself.

I have typed Cmd+T to see the extended tags box.
I have added "ISRC" as a tag.
I have entered the ISRC number which I received from CDBaby.

Is that all there is to it?
So is the number now embedded in my file?
It shows up in the extended tag box, but I don't see the ISRC number in the tag panel or the file information below the toolbar.

When the process is complete, do I use either the "copy to" or "move to" command to send the wav file with proper tags to another folder in my finder?

Thanks in advance

There is no automatism to show all fields from a file in the tag panel.
You would have to add an object to display the contents of the ISRC field manually.
See the documentation on how to customize the tag panel:

Thanks. I'm not so concerned with where the ISRC number shows up, as long as it really is embedded in the file.
It does show up in the extended tag box when I type cmd+T.
Does that mean I have successfully embedded the ISRC number?

Yes. Mp3tag has no place to store tag data except in the files - there is no cache or database.

OK, great!
So, has the tag data been stored in the original file I loaded into Mp3tag?
It looks like that it true, because when I click "show in finder" it shows the file in its original location.

Exactly. The modification is saved directly in the metadata that is part of the file.

Thanks for your help and your patience!
I believe I can get this done now.