Here’s one that I found pretty recently, it’s the sort of thing that hides in plain sight and blows your mind when you finally connect the dots in your head.
So if you have some knowledge of the production of the original Star Wars, you’ll know that the Falcon’s early design was ultimately repurposed and used for the (much larger) Blockade Runner. It would have had a linear interior, basically a single hallway running the length of the ship.
It wasn’t until I saw the following production image that I realized the interior set design from the abandoned “linear falcon” concept made an appearance in the finished film. When compared to the sketch it’s almost an exact match.
I assume that this particular set was built as the Falcon’s interior, and quickly redressed for use as Princess Leia’s ship. This would mean that the Falcon’s original design made it way further into production, which is something I was absolutely unaware of. It’s just weird to think that the famous scene of Leia putting the plans in R2 technically takes place in what was once the Millennium Falcon’s interior.