The Elderly didn't know how to 'create' an Abnormal, but the 'Archbishop' clearly did.
He just instructed the Elderly to follow his orders, and the orphanage naturally generated an Abnormal space.
Seizing the red-dressed doll was also an order from the Archbishop.
The anomaly of the Endless Corridor was not created by the Anomaly Sect, but after the Elderly sent someone to explore and report the information, the Archbishop sent the 'order' to take away the red-dressed doll.
Although the Elderly didn't know the reason, it was clear that the red-dressed doll had some use for the Archbishop, so he was also diligent in handling it.
But apart from that, the information the Elderly knew was actually not much; he was just a tool, following the Archbishop's orders.
He took advantage of it.
However, this Archbishop was not like some 'enemies' He Ao encountered before who erased their existence through certain means, but almost completely existed in the Elderly's memory.
