Filter out unverified leads from lead finder

When using lead finder, I'm finding that after importing a certain amount of leads and getting them verified I'm left with a certain amount of credits, when I go back into lead finder to import more leads I'm not getting the new contacts but instead it starts at the old contacts that were already previously unverified and I'm left with the same small amount of leads verified. I want to use up all my lead finder credits but cannot because of this.