When I was updating a mod for displaying meteor seasons, I encountered multiple vanilla meteor seasons (iron/copper/gold) appearing at the same time. I thought there is a bug in the mod, but I've tested the case and revealed different metals falling during one (two simultaneous, actually) meteor shower. I think it isn't supposed to be like that.
Play the game and wait until seasons overlap.
I attach a save where two meteor seasons (copper and gold) are active.