Very interesting thread!
My board has also some inconsistencies. Most of them where created during an reimport of postings.
The 6.2.x versions have some bugs with the replies count, but they should be resolved in the 6.3.x versions. I'm currently updating my board from 6.2.3 to 6.3.2, so I can't say for sure.
Deleting posts seems to be a weak point in ubb.threads. I think that this caused the inconsistence regarding posts, replies and threads count.
Have you already made some queries/scripts to repair the errors?
Sharing them would be very appreciated.
If you need some help, test data etc. just let me know.
