(In fact, if you see three dots " ... " at the end of the "To" listing, then not all names are shown.)
Thanks CJ, you have described the situation correctly - a number of recipients followed by an elipsis.
On further inspection I can also see that all these posts are from the same Freeper, who was part of my first thread, so clearly I'm on his ping list. I had not been observant enough to notice that before.
In a way this fact is another piece of input to the original subject of this thread - a Freeper noted my interest in a particular subject and has pinged me to all his threads on the same subject since then. I'd call that a pretty helpful and welcoming thing to do, even if I was not savvy enough to recognize it!
Thanks again CJ for helping me "de-bug" this one.