There actually is a fairly easy way to test if the absence of more recent data from a number of stations has a significant effect on temperature records. If stations were purposefully dropped in favor of those with greater warming trends, one would expect to see cooler temperatures in the stations that do not have temperature records available in the last few decades than in those stations with a continuous record up to the present.
The chart below shows this analysis for all stations with continuous records between 1960 and 1970. Of the 1,419 temperature stations containing data for this period, available at the
National Center for Atmospheric Research, 1,017 continue up to at least the year 2000, and 402 stop providing data at some point between 1970 and 2000.
There is no significant difference between the temperature from discontinuous and continuous stations, suggesting that there was no purposeful or selective dropping of stations to bias the data. If anything, discontinuous stations have a slightly higher trend over the century than continuous stations. This result strongly suggests that the discontinuity in station data results from having inadequate resources to gather those records, rather than from some pernicious plot to exaggerate warming trends. (ibid)