Sellers on the 'bay are not always builders/collectors of Models.
They Just sell them.
Promo's were available through Car dealers are advertising. You could get
them Free for a Test drive, (Or even by just asking if you were a Regular Customer)
or Buy them for less that $2.oo most of the time.
As such, they were not kits, but already assembled and painted (2 tones had the second color painted.
Some had the Aluminum/Stainless painted silver.
None of them had exterior trim parts other than Fender or Hood ornaments.
Side mirrors, fender skirts like on your Bonney, the Side Pipes too, and anything else
like that were added to the tooling for the Kits.
As for why they tend to be called both interchangeably, look at the chassis of your Bonneville.
Notice the 4 screws that connect the chassis to the body.
Almost all promo's Still use those, so a seller who does not Know Models like we do will
presume that he had a promo and not an Old Kit.
Especially if the kit does not have an opening hood and engine
(Which None of AMT's had till 1960--and then Not all got them)
Look at the re-issue 61 Ford Galaxie, No engine. Many will call it a Promo if found built
even if it has a Custom grill, etc
MPC still used the screws on Annuals to the 72 year. My Chevy Cheyenne Pickup had 2
through the front of the chassis into mounts that were part of the radiator wall.
I believe my 72 Impala still had 2 at the rear of the chassis.
I am not sure if my 73 Caprice still had them, but I can check.
Checked---- They are not there, but the mounts are still inside the body, the depressions
are in the gas tank on the chassis with pins on the inside of it to into those screw bosses.
I am not sure what year AMT dropped the screw assembly from Annual kits.
But if you look at some of the older re-issues, like the 62 Buick Electra, 64 Comet Caliente, 70 Pontiac Bonneville,
The screw assemble is still there.
Most likely since these were never re-issued during the time AMT & MPC stopped using them in kits.
If all you see is a Body picture of a model, and want to know if it is a kit or promo, just look at the shape.
Older Promos will shrink due to the Acetate plastic used for its high gloss shine without painting.
AMT changed around 61, but it was not as glossy, so they had to paint the primary color, which lead to
them changing again within the year.
The Shrinkage is what leads to their Warping. The plastic shrinks more on one side or surface than another
and twists,sags, "Smiles", etc show up.
I have a Nearly perfect straight 59 Ford wagon promo, that though it has shrunk, it is still Very straight. The interior
though is Twisted. Here:
After 62 or 63, Promo's will only Warp if Melted. ie left in a clear show case outside in the Bright sun too long
or subject to some other heat source hot enough. Kits will too!!!
I have Both is that condition (The Mustang promo I bought that way)
There is a lot of information about kits versus promo's out there.