I got it fixed by Technorati support. There does seem to have been an ongoing issue, as I found another blog which has a very good article on it: http://consumingexperience.blogspot.com/2005/06/technorati-tag-pages-problems.html
There were some updates that didn't get through when they sent the spider back to reindex my site. Namely it picked up all the new but now archived posts but not the archived but changed ones.
So I tried out the method on consumingexperience, making all my posts appear on my home page, and sure enough the updates were picked up on pinging technorati.
Now I have been having a problem getting into their Blog Finder, despite having tagged my blog profile. So I am going to try an alternative method, using "tag directory" tags (like the ref="tag" ones but using ref="tag directory" and the href pointing to a directory service: I used the technorati one, but any will do).
I placed these in my about page, but technorati doesn;t index this so I am going to set my home page to a "static page" in the wordpress options and point it to the about page then ping technorati and see what happens.