The USCRN is a new network of 143 stations that wasn't fully completed in 2008 (started in 2001 with data becoming available 2004). The data prior to 2004 is from the historical sensor network (USHCN).

The whole reason the USCRN was built was because of the problems with the historical network. The USCRN was designed to get more reliable measurements.

The aforementioned spreadsheet illustrates the problems with the USHCN data.