Trust me... there are
Its much harder to keep tab on every single little thing you had in mind when you put things in motion or create a scene, a conversation. 2 months later of the original idea you can easily find yourself coming up with an another explanation why those two were doing those things the way they did in your own darn game
Of cours this never happened with me. I keep ..like.. everything in control!
But on a more serious note, the ionian coin is exactly the type of thing thats either have a very deep importance that the dev may or may never explain in full detail while he himself weaved a whole story around it.. or it was just a flashy moment to throw in. Both is equally possible. Obviously we'd prefer the former and that has the higher chance. That it has a meaning, a story, a future in the game.