Not all hard tops had lead seams at the roof quarter panel meeting area.
Sometime in 70..probably late production/early production 71's, vinyl top cars had this wierd chalky type of a body filler material. My car was one of them. I know this to be since the car was original when I first got it.
Most likely, a team of two workers worked together on each side of the car doing the lead work on the assembly line.
One would heat the panels, clean and any other prep work help needed and the other would apply the lead and smooth.