Batches are not a formality here. Which harvest, which tank, which bottling date: that has to hang off the product, because it's printed on the label and because if there's ever a query you need to say what went to whom.
Shipping oil is logistics by weight. Bottle sizes, pallet rates and postage by quantity need to be stored, or every larger order gets recalculated by hand — and almost always too cheaply.
Regulars reorder, but only if you remind them. Somebody who took five litres last winter runs out in the autumn, and a message when the new harvest is bottled is the cheapest order of the year.