I received my D800E #300778X from Amazon around October 15th. Its serial# is newer than the one you just received from B&H on Monday.
>1) It's still not clear if there is a D800 out there with serial number 3007505.
I seriously doubt that. Any mfr that would make a serial number contingent on a "style" number would be asking for trouble. If that were the case, the style number would be part of the serial number, not independent of it.
>2) Why the discrepancy in serial numbers in so-called "just released" D800E camera's from both Amazon and B&H?
I think "so-called" is the operative phrase here. One must also ask, just released from where?
I doubt that any cameras are released from the Nikon factory in Japan and shipped directly to retailers. It's likely that Nikon imports cameras by shipping to a US distribution center which in turn ships to retailers, which in turn ships to customers. With each step in the chain of custody it is also likely that cameras are not chosen to be shipped by the order of the serial numbering, but by the order in which they are placed in stock. IOW last in/first out -- first in/last out. Furthermore, it's likely that cameras are originally shipped from Japan in pallets and that the pallets are split when retailer orders are fulfilled.
I don't really know how Nikon distributes its cameras, but it doesn't surprise me that there's no rhyme & reason behind the order in which customers receive new cameras.