Ignoring a host of other issues about TOBS, according to USHCN V2 docs the USHCN V2 TOBS adjustment is supposed to look like this – positive since 1980, and slightly negative prior to that.
This is somewhat similar to V1 (dashed line below) except for a different offset, and a smoking gun of very different behavior after 1990.
But the actual implementation of V2 TOBS (thick blue line below) is very different from the supporting docs. The actual adjustment is about 0.2C lower than the graph in the specification (red and thin blue) lines. It is abundantly clear that their code does not correctly implement the specification.