Sounds lame I know, but I was switching out my back dome light and noticed the headliner doesn't appear to have the hardboard backing that I figured it would...

It has the thick insulation looking material but I stuck my fingers back in there and I don't feel any hardboard...

there is another hole above rear seats, same thing no board...

Does anyone know if they didn't come with hardboard on certain models??

It appears all original and unmolested...

 

If it keeps it's shape, it's got to have something. The one I redid was some sort of foam/fiberglass material about 1/4" thick. The headliner material with foam is about 1/8-3/16" thick and should be directly bonded to the board.