CWOL, I'm not Cadet, but I am a long time poster, i.e., 16 years to be exact and the rule of 100 postings has been in effect for as long as I can remember. One of the possible reasons for the length of threads is software limitation and yes, they do come along a couple of times a year and clean up the main frame, which means older threads do get deleted from the main frame.
Actually, it's not difficult to track back to the original thread if you link "new and previous" thread links. That's why Cadet and I have been coming along and reminding posters to start new threads and put the links in or putting them in for posters. Some posters have gone the extra mile and posted all of their links into new threads so that the entire history is available if a new poster wants to see the history.
Some day, they may get a new database that will be able to hold more data. Many of us have lost our threads over the years due to purging and that's another reason why posters should print of their threads or copy them to a thumb drive.
Also, if someone is interested in your history, they can do a search on your name and find all of your postings as well as clicking on your user name to find your postings.
I'm sure Cadet will have a better answer than mine, but linking threads for now is the best way to ensure that everyone can read all of your thread history, not only in this particular forum, but all of the forums if you opt to post elsewhere.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.