I have and have owned multiple survivor cars, cars with original trunks and one owner cars. The cars I own or have owned are '66 Chryslers, '68 Furys, a '70 Fury, a '70 Polara, '71 Furys and a '72 Furys + I have several friends that own and have owned many Furys and C Body's from '67 - '73 so what I am going to say here comes from over 25 years of experience owning, working on and restoring C Body cars, mainly Furys.
The factory painted the entire trunk area, floor, wheelhouses, inner quarter panels etc. body color first. The factory then sloppily applied trunk spatter paint to the inner quarter panels, the inner wheelhouses, the brackets holding the trunk hinge mounting panels, the trunk floor quarter panel extensions and the area around the spare tire mount on non-convertible cars.
The splatter paint was applied by hand with a spray gun in a sloppy manner. Usually, most of the inner quarter panel, wheelhouses and trunk hinge mounts got a good cover with a sloppy overspray onto the trunk floor quarter panel extensions. Sometimes the splatter paint covered part of the quarter panel extensions and sometimes it extended part way onto the trunk floor. They basically sprayed the spare tire mount with a couple of passes with the paint gun so some cars have a larger area covered than others. No masking was involved.
'68's used a dark grey spatter paint while '70 & '71's used almost a black colored paint with aqua/turquoise specs in it.
The spatter paint needs to have a clear coat put over it if you want it to last.
Feel free to contact me with questions.
Bill