@aclare87,
I've never dealt with trade discounts, as distinct from a discount for early payment. I went so far as a brief scan of Uniform Commercial Code, and my very old intermediate accounting text and found no reference to a time limit on trade discounts. I did find reference to varying levels of discount based on the size of the order, but nothing based on timely payment.
Just because I didn't find it doesn't mean it doesn't mean it doesn't exist.
A minor clue might be found in the software I used to use. Peachtree Accounting allows the vendor to set up different pricing levels for each customer. Quoted pricing is not dependent on either the size of the order nor time of payment. Also, some businesses, like trucking companies, have a stated rate, and virtually every one gets a discount. For some reason, they think this is better than constantly revising the listed price, or rack rate as it is usually called.
Sorry, aclare. I don't think my replies answer your question. Hopefully, you can find someone in retail who does payables.