I encourage people to look into the ERA5 dataset provenance especially when you approach the observations made toward the "pre industrial date" of 1850 .

Remember that modern global surface temperatures are collected by satellites, and the dataset is comingled with recordings observed visually & made by hand using buckets by sailors who were not primarily academic researchers. Segments of high resolution, low noise data (satellites) are mixed with low resolution, low coverage, high noise records (hand records on a boat made surrounding the united kingdom).

My point is to be in awe of the technical aspects of this effort but also keep in mind that we are only making copies of low resolution, noisy manuscripts from sailors 170 years ago.