I haven't seen the Dwarven crown crates in a solid year now. So i think they should work more like this
Monthly Rota
New Crown Crate (4 Weeks)
Old Crown Crate (1st 2 Weeks)
Old Crown Crate (2nd 2 Weeks)
this would mean that each month we have at least 2 previous crown crates because having to wait a year for like pet I want.