I think I understand now....
I had this box checked
Receive reply notification only for the first unread reply.
So, if I never looked at that thread when I was notified, I probably wouldn't receive another notification because the software thought I never read that first unread reply, so why would it send notifications for additional unread replies after the first?
Well, I unchecked that box, so I think I might receive notifications for everything now which I what I had in mind -- A notification every time someone posts on a thread I'm watching.
Otherwise, as Nilsjohan suggests, I could "refresh" my notifications by going to my profiles, under Notifications and emails, and clicking each link. Sounds like a lot of time though, so I'm trying unchecking that box. We'll see what happens...
.... I also see this in the email notifications...
More replies may be posted, but you won't receive any more
notifications until you read the topic.
Bingo! Although I wonder what will happen now that I've unchecked that box.
I see the light! (I think)