Across mopar, not necessarily just Hamtramck plant, I have seen sheets under carpet, in headliner, behind glove box, in all seat springs, behind netting against foam, under the asphalt vibration mat on the top of the fuel tank.
I've seen the sheets screwed down to the floor of the cars so they didn't disappear down the assembly line. I've seen several pieces in this location represented by only a small piece that is still screwed to the floor after the line workers pulled the sheet up and threw it away.
On another note, I've only ever seen a hand full of "BUILD SHEET"s found in any of the cars. Build sheets are quite different than broadcast sheets and are a thousand times more rare than broadcast sheets.