Prolong Surprise Mummy

I thought we are not going to see surprise mummy until next season? It seems some clans still able to prolong surprise mummy . Any idea ? Thanks

 

“Elite Boosts beginning with 1.9.0 can only be prolonged until the end of the next War Season in which the same Elite Boosts will be given as rewards.”

 

Mummy boost wasn’t a reward for last season so it could be prolongued normally.

 

I see. Thanks for the reply