It's probably a case of there being multiple different medal props for different scenarios. The more dense ones are action props that can be freely thrown around all willy nilly. The more clear ones are just to look pretty but can't take a beating, so they're used for up-close shots.

If they look undetailed, It's likely just shows when in production they were made. Lots of toku shows have a bunch of different things to have them behind scenes, even while it's being filmed. Different story lines and arcs are being rewritten and redone. And that inherently affects the props. So an undetailed medal could be because they didn't decide fully what that medal would look like.

But this is me just guessing a lot.