I have never had an issue with the NOS clips and NOS rocker panel molding. The front end clip (the one that holds the stud) snaps into the rocker panel. It should be a tight fit and not loose like the crappy reproductions.
As for installation, the approach that you mention from Charles has worked for me. I first align the rocker panel front with the clip with the stud going into the fender hole, then more or less set the rocker panel on the top of the rest of the mounting clips, making sure to catch the edge of the rocker panel to the clips. Finally, with a firm press of my hand on the bottom of the rocker panel on to the bottom edge of the clips, I snap the rocker panel to each clip from the front to the back. Sometimes I have to hit the panel with the outside of my fist to snap it it place, but not a knockout kind of hit!
Regards,
Pete Morgan