How to remove no longer used Grouping string? iTunes 12.9.5.5. (and earlier) Grouping field issue.

Almost since its inception I have used the iTunes Grouping field to hold unique strings (e.g. Complete.Album) to allow for the creation of smart play lists based on those included strings. I often have several strings in the field which are comma separated (e.g. Complete.Album, Grt.Amer.Sngbk). At some point in the past I entered an uncapitalized "complete.album" and "complete.album, NNNNNN" and - then later I corrected those to be capitalized. Now in some cases iTunes has started to autocomplete to this lowercase instead of the desired format. Nit Picky I know but it is an oddity I am trying to fix.

When filling in the Grouping field via the information pane "complete.album" is offered as an option yet it no longer appears anywhere in the iTunes database - well at least not in the XML data I can parse.

I have also done a dump via File/Library/Export of the database and searched for the lowercase string "complete.album" and it does not exist.

In general when you stop using a string in iTunes it no longer offers it nor does it appear in the pattern matching list.

I have also looked at the Work and Movement tags as I recall Apple did the Work/Grouping field switcheroo a few versions back. Nothing there.

So can I be lucky and is there small file someplace I can just edit this out of? No I am sure not. I have by now used several scripts to look at all the typical text fields in iTunes to see if I entered it in one of the others e.g. Genre/Artist/Album/etc.

Stupid little bother but now wondering if it is embedded in a song (are there retired tags?) where I can no longer see it. Or it was in a song which has been removed and thus there is no pointer to it.

Any ideas are welcome. Thanks.