The factory installed the headliner before the windshield or rear glass. That being said, a real good installer can put in a headliner without removing the glass. I had two 66 headliners (Fastback and a Hardtop) installed without the glass removed. My secret installer was one of the San Jose assembly line workers that did headliners before he retired. I saw it done, and it's a lot of technique, tools and skill, but it can be done.
Jim