Seemingly Random Orders Not Taxed

I have a pre-order setup ($15) which is marked as taxable in the product base.  I currently have 91 orders for this pre-order.  89 of them were taxed, however, two were not.  I force account creation upon checkout, and the zip codes provided for the untaxed transactions are local (taxable) like many others (in other words, they aren't out of state or anything).  Trying to figure out how these folks got away without paying sales tax. 

Do they have the correct state selected on the order? It calculates on the state selected, not the zip code unless you imported a list of zip codes.

State looks correct (Georgia/GA). 

Not a clue why then. You can email me the following for me to look into it: 

• The link / URL to your Sytist admin (where you log into your Sytist admin).
• The admin username and password (or create me an admin account by clicking Admins in the upper right corner of the admin pages).
• Link, username and password to your HOSTING control panel so I can access the database directly.
• The 2 order numbers of the orders that were not charged tax.