school me on differences between Dart, GT, and GTS?

Found this Dodge Dealer Data Book on Barry Washington's Hamtramck Historical website http://www.hamtramck-historical.com/dealerships/1969DealershipDataBook-05.shtml As usual, Barry has a lot of good stuff over there on his site. Anyway, the Data Book gives a brief overview of the different trim levels. Doesn't seem like much between them - just different styles of stainless trim and badging and available options. If I'm reading that Data Book right, it looks like the 'vert was only available in the GT and GTS trim level - is that right? For some reason I thought that grandma could have ordered her base level Dart as a drop-top if she so desired?