It's not "Pink Vynn"

The list obviously is incomplete. I still believe the Silver Medals are permanent while the Gold's are not.

This can easily be backed up since most of the gold medals we see have nearly been confirmed to expire, and most of the silver ones expiring wouldn't make any sense, especially the Level 200 ones.

Exactly. All of the gold ones are competition medals. You have to compete with people to get and keep those medals. For the boss hunting medals, you have to kill more of that boss than anyone in your server to get that medal. For the Donator medals, you must donate more money that everyone else in your server. For the Maple Idol Star medal, you must collect more fame than everyone else in your server (1k fame within a month is required for the quest to get the permanent medal). The other gold ones are just like that. You must compete with people to get them. Most of them are a waste of time trying to do and some are near impossible to do.