Ok, I think I found the key in all this so I thought I'd post it here in case anyone else runs into this. In the files I've been referring to, they keywords are being stored in the IPTC field of the image. It would appear (and I have yet to fully test this) that if you delete those keywords from within LR Classic, LR Classic "kind of" filters them out so you don't see them. Now I'm a little confused about that because when I look at the IPTC fields in LRC, I don't see any fields that say Keywords, so perhaps the Keyword Pane in LRC is the IPTC field for the file. However, that doesn't explain why after deleting the keywords in LRC yesterday, then copying that image over to a test folder and opening it in Bridge today, there is still has an IPTC Keywords field and it's populated with the keywords that I had deleted in LRC yesterday. Obviously there's a lot going on there that is escaping me. Nevertheless what is happening is that I was deleting them (or trying to) from Bridge's keyword set, but as I did so, Bridge would refresh the image and in the process, re-read in the IPTC Keyword field and "pop" - there they would be again. So while I'm still confused (a fairly steady-state situation for me these days 😉 ), I do think I've stumbled on to the reason why the things I'm seeing are happening. It is a bit odd that when Bridge displays the keywords in it's keyword pane, why you can't adjust the IPTC keywords from there; and perhaps this is how it's supposed to work, but for some reason, isn't. There is still more to discover in this, and I'll keep at it but for this thread's purpose, if anyone is having troubles with keywords in Bridge, I would recommend going to the IPTC Core section, selecting the keywords in the Keywords field and deleting them from there. Then you can go back to the Bridge Keyword Pane and proceed as you normally would. By the by, I subsequently added a keyword a few keywords to 2 of the files I was having issues with (after first clearing out the IPTC>Keywords field manually) and those did populate the IPTC>Keywords field as expected. I then cleared them from within the Bridge Keywords Pane and they did clear as expected. The mystery remains as to why I haven't been able to clear (or easily clear) the IPTC>Keywords that came with the file via the Bridge Keyword Pane, but at least this offers an explanation as to how to clear it if you're running into this issue yourself. The investigation continues, but this does resolve this problem, if not fully.
Thanks again for the help Lumigraphics & Stephen. Much appreciated.
EDIT - Addendum: I discovered that there was one folder I had not eliminated the keywords from and voila, I suddenly had a keyword list as long as your arm again. Fortunately it only took a minute to delete the unwanted keywords, but unfortunately it left a bunch of left-over keywords in the keyword list again that I will only be able to delete one at a time as they are not in any metadata field (obviously). They weren't assigned to any photos so it was easy to delete them, but nevertheless it was a very time consuming process. This tells me Bridge does not have a dedicated keyword list and everything just goes into (and comes out of) the IPTC Core>Keywords field. It also tells me that while I might have a nice, compact list for the images I do need to track, that list will suddenly grow to "x" proportions as soon as I click on an image outside of these folders and which may have keywords embedded themselves. That just doesn't work for me and thus the keywording setup in Bridge really isn't of much use unless you have a completely unified setup, such as a single stock listing with nothing else from other sources. Unfortunately for me, I also have digital art, Illustrator files, etc., etc. Those need a totally different set of keywords and since Lightroom will only read pixel based files, I have to use something else to deal with those files. I think Finder will fill that role for me quite nicely. Anyway, hopefully this thread is of use to others who may be experiencing similar frustrations. Thanks again to responders. I appreciate your time.