zIWT posts are numbered sequentially. Start at '1' and work your way up to '65304'.
The only gaps you will find are those created when the database interface library went south and we had the 'posts that are too long go into never-never land' bug. That interregnum will be quite plainly demarcated by the test posts.
Or, come up with the supposed post content and we'll employ the search tool. Not nearly as conclusive as the above method, however.