Just posted a group pf pictures in response to the same basic question about interior door paint details. Though I should post some of those pictures to this tread while I had them handy. Might be a little duplication but I don't think that will hurt the thread
As mentioned above the interior paint was applied first. For 65-66 this means the doors, dash and A pillars. These areas were then masked off either free hand or some form of precut mask that was tapped in place. Because of this you can get areas where the paint (exterior color) could blow under if not tapped or the mask lift for a section and produced a softer paint edge
At the rear most of the edge is located where the weather strip would be attached except at the very top at the rear where the paint extended further as shown

And at the bottom of the rear edge the mask/tape pulled in and away from the weather strip impression in the door edge.

This could be done neatly or a bit messy with ends and pieces of tape in the say as shown
As we look at the bottom of the door we find that the mask did not follow the weather strip impression and track area. Instead we often find a straight edge produced from the taping of the mask or in some cases a less than perfectly straight line. Also painters, either interior or exterior ones, didn't always put the effort in on a particular car to bend over far enough to apply allot or in some case almost any paint to the bottom edge making the paint lines difficult to see. On other examples a good coat of paint was applied as seen in the pictures below

Not much paint for interior or exterior on the bottom of the door on the left while on the right a nice coat of both on this example

More difficult to get pictures of the front edge of the door but here is an example. After the transition at the forward bottom corner like at the rear the paint line travels to the weather strip impression then takes a straight line to the upper weather strip impression and into the window opening from there

Though it may not matter since its an unseen detail, for what ever reason San Jose workers choose not to mack off the center of the door surfaces where the door panel would eventually be attached

Hope this helps others