Paz pointed out that the normalization used previously might not remove geographic biases introduced by fugitive weather stations, so here is another approach. I have differenced each of the records, averaged the differences and then cumulative summed the result.
This way we are dealing only in annual increments, up until the final summation. The result differs from the previous, as the pop-up in 1914 is lowered, and the temperatures post 2000 are raised. However, it still seems to depart somewhat from the official version.