When I last looked them up, the organic standards said you couldn't use wormers prophylactically (that is for prevention), only for treatment.
Verm-x is a herbal, I am sceptical about its efficacy, but am willing to be persuaded, I am no scientist !
Therefore the organic route would be to purchase a worm count test kit from SfS (Supplies for Smallholders), test and then only treat if the count justifies. But as you say in your case you are probably out of time.
We worm weaners as standard, at least then we know that they have been treated before they left us. Our last egg count from a sow was none found.
In your situation, I would tend to ask the purchasers what they want you to do, and leave the choice to them. If they say no, then they left you with the purchaser knowing, if they say yes, then they take responsibility for them adhering to standards, and jab them with a wormer. If they want you to use verm-x, then you can start this.