I haven't bought the 3rd offer one yet...it brought up the Exterminator's Super Glowing Sparking Arm Cannon of Instant Death as a new one with a tag stamped over it as "Already Owned"
Didn't even know there was a 3rd offer available
If you complete the Cursed Child Tier 4 11th objective from Mugwarts, it unlocks a 3rd Golden Item to rotate in the Challenge token store.
It's usually good at choosing the 2 Golden items to display. Do you own almost all Golden items that would be available from the token store currently?