I discovered that some old threads were still marked instant notification in the list at Quick Links > Subscribed Threads. I checked them and selected no email notification in the drop down menu and clicked go. Then Instant notification changed to None. Hopefully it will work. I think setting "no email notification" like I originally did just applies to future subscribed threads. Notification for threads subscribed to in the past has to be turned off in the way I just discovered, for each thread.