Copied & pasted or synched files - custom field includes other field information

[The Incredible Boom Boom]

Please can you also tell me how you got  WORKSUBITLE and STYLE as that is not available in my dropdown list for defining a custom tag.

I do not wish to be rude but it is not nice to be talked down to for misreading or not understanding messages.

How to Create a Custom Tag

If you want each role separate, you must "define new tags," as presented in the first link I provided you (if you had looked at and understood @hiccup's write up, you would've understood the difference between using pre-defined tag versus defining your own),

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It is normal to use KISS when trying to explain something that is easy for you just in case the person reading the information is not used to the "terms"

More accurately, you've named a Custom Tag associated with the real tag "Involved people list" "Producer."

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It looks like from a lot of reading, experimentation, rereading the messages and rereading again - that i should define my custom tags as "save to musicbee database only"

"Save to MusicBee database only" Custom Tags are equivalent to separate Custom Tags saved to files.
You can format a "Save to MusicBee database only" tag as role:person;, but it's not required - only the "Involved People List" tag requires this format.

Changing the producer named tag to IPLST (or another title) and define as Involved People List

Yes, then remove "Involved People List" from all the other Custom Tag definitions.

Then start the long process of editing names to role:name - where role is one of my custom tags.
That may populate my relevant custom tags "fields" with the information.

Or...

I personally would bypass the manual input (that's what really is time-consuming) and learn to use MusicBrainz Picard, as many of the albums you've tagging likely already contain the desired information in the MusicBrainz database. If not, you could add the roles to the database yourself (so others can tag their tracks appropriately) and then use Picard to grab the tags for your own files.

I believe it'll be less time consuming using Picard to add IPLS roles to all your tracks, than inputting them manually.

[tosmcgee]

I believe it'll be less time consuming using Picard to add IPLS roles to all your tracks, than inputting them manually.

Don't think i have not tried it. Unfortunately quite a lot of the performer and techie info i put on is not there or else the track is not to be found through picard so there is a lot of manual work regardless.
I have eventually found the "Define ... " button on your link and my apologies for not understanding then, and perhaps still not understanding now, what information you are trying to get across. It may be helpful if the section on the virtual tags were on a seperate page to avoid some confusion.
I am not using "Save to musicbee database only" but it is too late - by using "Save To Musicbee database Only" for that short period and then changing to their new defined tags has led to blanking those custom tags on one computer anyway - i am trying to see if they are still available on the other computer (I doubt they are)
I have been able to copy a few files and check if the tags stick with the file and they appear to do so. So i can am in position now to move on from here and look after the newer files, maybe over time i will try reinstating the info withsome help from picard if i can find the relevant info.

I think i can be comfortable now that when i sychronize files my two computers that the tags will not be abused.

[The Incredible Boom Boom]

I am not using "Save to musicbee database only" but it is too late - by using "Save To Musicbee database Only" for that short period and then changing to their new defined tags has led to blanking those custom tags on one computer anyway - i am trying to see if they are still available on the other computer (I doubt they are)

I was afraid it might do that, especially since the "Involved People List" tag was being modified each time you edited it under a different Custom Tag name.

I have been able to copy a few files and check if the tags stick with the file and they appear to do so. So i can am in position now to move on from here and look after the newer files, maybe over time i will try reinstating the info withsome help from picard if i can find the relevant info.

Good luck!
Another benefit to inputting missing information into MusicBrainz, then saving it to your tags with Picard is accidental information loss from tags becomes less frustrating.
Just something to keep in mind.