The message count should be correct for the messages marked as unread but may not be 'correct' for whether you have read them or not. Some may have been imported as unread and then read on the old site (hence the mismatch). I think a "mark all read" should solve the problem.
Save with the post counts - there are some repeated posts within a topic and uncounted topics and posts which will be updated when I run another job. Trying to have a live import running and kept up to sync while using a site live was problematic.
I'll be adding a 'topics posted on' soon, there is already a 'topics started by' facility.