Apparently the Amazon system is now using somekind of non-published data to vet shipping delivery dates.

This flaw, allows a buyer to select a ship method when purchasing that the system will NOT allow a seller to use. How is that possible???

example; buyer selects a premium 2-day ship method (this is a FBM order)

The Amazon system used a promise date that was 3 days from purchase date, seemingly enough time to meet the delivery promise. However, when trying to purchase the ship label (on same day as purchase) through Amazon, the system would only allow one carrier option, which was significantly more than the purchased/selected one. It would not even allow me to use a 1 day delivery method

The explanation that was given to me was that "....Amazon uses internal transportation data and high likelihood of meeting the buyer’s delivery promise to surface ship methods. It is possible for a ship method to be available on a carrier’s website and not available on Buy Shipping. This is reason your preferred carrier is not available in the Buy Shipping option.

Why is it not using this logic(???) during buyer purchase??????