Here's a possible variation on the idea. I'm not sure of all the positives and negatives, but kick it around a bit.
Each "year owner" starts a thread for his year. He makes the first post, which will be the history for that year. He keeps adding to and editing that top post. Others can comment, suggest refinements, debate, etc. in the thread below. When the owner thinks it's "ripe" a moderator can import the top post consisting of the year's documented history into a locked HI history thread.
The locked HI history thread could only be posted to by moderators. It will stay clean and provide one-stop-shopping for someone interested in the history of HI.
This is an excellent idea. It keeps the HI history thread stable and in a sense, "official." It insulates the history thread from differences of opinion that might arise over what to include or not include, while allowing forumites to discuss those questions in the yearly threads.
I wouldn't anticipate many differences of opinion, but there are bound to be some, and Howard's idea lets them run their course without bogging down the main project.