I need a little clarification regarding the Bulk Upgrades...

I would like to know if the Pro Sites Bulk Upgrades module allows users to use credits for upgrading from a Pro Site Level A to a Pro Site Level B.

After having tried it out, it seems that it only allows the use of credits if the site is being upgraded from a Free level to a Pro Site level. But, since I don't have a Free level available, I'm not able to test this, so I'm not sure if that really is the case, or if my setup isn't working right.

Could someone please clarify this for me?