The sql file that comes with this mod does 3 things:

It adds a tinyint called COWOA_account (1) and COWOA_order (2) to the customers and orders tables. I haven't looked at the php code but I presume this is used as a flag to indicate if an account/order is a COWOA one. It also adds a query to the query_builder table to allow you to send emails to permanent account holders only.

Remember, although this mod says you can buy without an account, it's not really true. It creates an account that you cannot log in to and makes sure you do not receive any correspondence from the site. The modified code uses the above flags to differentiate between details it has for account holders and people who checked out without formally creating an account.

So, in summary, if the sql was broken, it wasn't this mod that did it.