Official rusty skins have specular maps, the rusty parts don't really have any reflections. you can see it using the in-game specular debug render mode
to add, if it isn't clear enough, here are some regular in-game pics (credit: node) https://cdn.discordapp.com/attachments/793909319959707698/831273929888890970/unknown.png https://cdn.discordapp.com/attachments/793909319959707698/831274353449893909/unknown.png