Jerbo,
Here are some definitions that might be helpful:
A regular production option is an option available from the factory (a "factory" installed option). Each RPO had a number ID.
A factory (or GM) accessory is an item sold by GM that could not be obtained installed at the factory but could be installed at the dealer (or, by the owner). Each GM accessory had a part number,
An aftermarket accessory is a non-GM item for your vehicle.
It is also possible that a dealer could have installed an item that was listed as a RPO but not ordered that way from the factory. In this case, the item was ordered by part number and installed by the dealer (or, by the owner).
Tim
