No idea... the previous owner told me everything was original
... that was before I knew a lot about GT/CS's. I had emailed him (the car was on eBay) asking about specific GT/CS parts and he assured me they were all original. I won the auction, he drove the car to me, and I paid him. He also gave me a copy of the 1996 Registry, and over the next day or two I read it and discovered several fake/incorrect parts that were ones I specifically asked about. We had some words and he ended up refunding me a good bit of money.
Anyway, the trunk lid's an excellent copy... the only giveaway is the visible fibers. Everything else (top, sides, frame) looks like it should. I do know that my end caps are original because I've pulled them and they are smooth all over. I suspect that my tail panel and side scoops are original, but I don't know for sure because I haven't pulled them. I do wish I knew who made the trunklid, because it could be a great repro part for the GT/CS. It could even be made to look correct with thin layer of bondo or gel coat over the fibers.
-Winston