I recall running a repair and compact on the database Sept. 1st, which was related to the DB crash of Aug 16th. This probably has something to do with the missing posts. I have seen MS Access DBs just drop records into nowhere when compacted/repaired.
Unfortunately, they are probably just gone. The forum is the last part of this site will running on an Access database which is far from ideal as reliability goes. I have tried several times to convert it to MySQL (which runs the rest of the site) but it is not straightforward. It takes hours to make an attempt only to find out that it failed again. Maybe I'll give it another go soon...