"Having the specs" isn't the same as "having the chips and boards and then running out because your suppliers can't keep up with your orders". That's what I meant.
But if you're collecting a bunch of orders and THEN using that money to buy the components, you have a pre-order model.
Pre-order model applies when you did not yet engineered or released the product to the market, and you're looking to do that with customer's money.
If a product is out-of-stock, but released to the market, that's back-log OR made-to-order model.
If you buy a BMW, you don't pre-order .. however they're assembling the car after you ordered it and the sales people get their commissions from your down-payment.
The manufacturer gets his money right after, from the financing institution (if any) .. and you're paying back what you owe to the financing guys.