Unnecessary no. of blocks

I created a Business Rule and placed a script set createnonmissingblk on; before it so that all the possible blocks get created before Business Rule send figures to required blocks. I noticed an increase of 6 million blocks in database. Then I ran a script clearblock empty; to delete all the blocks that do not contain data. That Business Rule brought no. of blocks to just 376 blocks. So only 376  blocks are the ones that targeted with data by this Business Rule.

Now I removed set createnonmissingblk on; from the start of Business Rule and again executed Business Rule. I was expecting no further increase in no. of blocks because all the blocks that could be targeted are already created. So running Business Rule again should not have increased any further blocks but actually it did. Anyone can help me to understand this?