Those look like a custom height panel, most likely made when the previous owner upgraded to a PX panel. SL has made custom width panels in the past so I’m sure they’ve also done custom heights.
As to determining if the panel is a PX panel, the earlier panels had no lattice structure between the vertical and horizontal ribs. The lattice greatly strengthened the panel.
Use a bright flashlight and shine it into the panel, you’ll be able to see whether or not the lattice is present.
See the pix. I attached to get an idea of how it looks.
And yes, that is a damaged panel, a story for another time.
John
