Request SE: Show "you had this" or "you dont have this" for mounts/minions

[Zomkei]

There is an unofficial plugin for the game that does exactly this, so that's fairly head scratching.

"Adds and indicator in item tooltips to show whether you have acquired that item.
This indicator is in the item's description near the bottom and only appears for items that are unlockable, such as orchestrion rolls, minions, etc."

the difference is that this plugin is client side, its not keeping track of thousands of players at once, but only your client.