I have done this for years.....
On vehicle windows that shift or traverse it is hard to get the "hidden" edge lined up. I began using a sharpie to make a mark on the film and the glass to align the film so that I don't push it too deep or not deep enough.
It works great on older cars like a 1968 Camaro where the rear sides roll down and you just can't see all the edges all the time but don't want to leave gaps.
Here is a picture of a 2008 Caddy Escalade door that I did today that had a "hidden" edge.

Film laid on door glass outside. Hard card the spot you want to mark to extract water.

Peel film back

mark the glass with sharpie. I use an H shape.

Quickly press film back down over the fresh sharpie mark. Mark should transfer onto the film and stay on the glass. I will remark the lines if it doesn't transfer or leave enough....
Align your mark when you are installing the film and you will KNOW where that blindside is and you will have the film right where you want it.
Film installed with mark still on. Just use rubbing alcohol to wipe off marks.