First, the matter of the Qing King's Blood Slaughter is purely fabricated.
Second, the Blood Slaughter activities, if they existed, were secretly carried out by the Qing King within the Qing State, happening in the observation blind spot of the Heavenly Secret Pavilion.
However, currently, the Pavilion Master's ability to discern the heaven's secret is beyond doubt.
The power of the Heavenly Secret Mirror needs no further elaboration.
Since the Pavilion Master personally used the Heavenly Secret Mirror to investigate the situation in the Qing State, if there were any conspiracies in the Qing State, they couldn't escape his eyes.
But, there were none...
This can only mean that there truly are no conspiracies in the Qing State, and it is not the location chosen by the Qing King for the Blood Slaughter.
Logically, then, the Blood Slaughter probably doesn't exist either.