This "authority" can just connect to some different points of network and log the blocks.
When the majority of the network is reporting one set of blocks as being accurate, and the minority is reporting a different set as accurate...
Wouldn't the authority automatically assume the majority?...
Looks like you don't get the idea.
That's the whole point of the service - to detect presence of the other set.
Detection is not a solution.
Prevention is.
It's DEFINITELY too late.