@DdmrDdmr, what does -91 mean in June post count for Indonesian altcoins. Does it indicate that during the month of June a total of 91 post on the Indonesian altcoin board were deleted?

Yes, negative numbers means the total post count of a specific board has decreased compared to previous snapshot.
This can be due to a number of reasons, namely
- Post deleted by user
- Post deleted by moderator
- Post moved to a different board
It is important to notice that whatever the cause, the posts that have beencdelted/moved, might have been posted earlier than the last period. I.e., regarding this specific issue, total post in June on that board might well be positive, but outnumbered by old post deletions by a moderator.