Basically, they are throwing out data that they don't like or does not fit their desired result.
I spent many years analyzing manufacturing process data for a major computer company. Engineers were always trying to ignore data points that were "outliers". Just because. I would not let them do that without an Assignable Cause. In many cases the outliers were their best friend to understanding out manufacturing process. But they hated having to do the work to understand it.
So it should be with this data set.
These “climate scientists” also refuse to use satellite temperature data which provides surface temperature data for the entire planet. Why would they refuse to use it? I think it is because they would not be able to manipulate the data.