A factory-installed A/C system would be expected to be installed in a specific way with specific components. Dealer-installed can usually mean several different scenarios:
-Dealer's may have installed it new and used the Ford kit. The Ford kit was not always a 1-1 with exactly all the same parts used at the factory
-Dealer's may have installed A/C, but the system was not the same as a factory system. The under-dash unit may or may not be the same as factory, hoses and other misc. parts might be different too. Sometimes the install can appear as a hack job.
Then, there are always owners who have installed A/C in their cars later on down the road. Some like to say since it was a "dealer option", then that's how they present it. Although, most of these seem to follow the factory-installed systems since most of the replacement parts available look like the factory parts.
It's kind of like dual exhaust. See lots of show cars with dual exhaust added and then the owners play the "dealer installed" card. The problem is when they add dual exhaust, they use all factory style parts. When the truth of the matter is if you asked your dealer for dual exhaust on your new '66 C code, they most likely would have sent it down to the local muffler shop and had them fab up and install a system.