I can explain all about Amazon (I’m a regular). When you order, depending what you order, it may arrive quite fast, or not.
If they gave you a discount for slow shipping, well, that’s what happens. You volunteered for that slow service. I never take the discount, I want my 2 day free shipping :)
Normally they are going to ship from the closest warehouse using fastest/most economical method. If they have all the time then they might ship using parcel post from an underused warehouse. Parcel post can take 20 days.
It seems so crazy that they could save THAT MUCH on a CD (it’s an aluum, ordered June 14, arriving July 5th), over 2 day or 5 day delivery AND it’s worth 6 bucks to them!!!
But I believe you.