For those of you who have not registered to the SISO discussions, please excuse this message. Currently, SISO-ADMIN is the most reliable way to the majority of folks who use the SISO discussions on a regular basis.
ListServ does not embed a unique thread ID in the subject of the messages like WebBoard did. It uses the subject (minus the text like Re: that is added when people reply) to group messages of the same topic/subject. When viewing a specific email, you can view by Topic and go forward or backwards to a previous post. If you want to see all emails related to that same topic/subject, then you need to access the Month view, located on the list page toward the bottom.
It would therefore be best for people to use unique subject lines.