To be included as a record, the NCDC has a rather loose requirement for including stations. Their website has some problems witht he map plotter at the moment, but if I recall correctly, there a station can be included if it has a 30-year record and each year has coverage of at least 182 days. Therefore, any station that has recorded temperature data for half of each year since 1984 will be considered as setting a new record.

Such as loose definition, however, is likely very misleading to the media, politicians, and the general public. When most people hear that a new “record high temperature” has been set, they usually have a longer period of time in mind. I suspect that most people would react differently to an announcement of a “record high temperature” if they understood that the records began when Ronald Reagan was president. Of course, it is convenient for political reasons to maximize the number of “record high temperatures” because it fits the mandatory narrative about global warming or climate change.

Skeptics have been quick to point out that many of the stations in question have short records lasting only relatively short time scales, so these so-called record temperatures are relatively meaningless in the context of the longer times that most people are thinking about. Skeptics are also quick to point out when even the skewed NCDC records go the wrong way. For instance, the fact that 2013 had more daily record low temperatures than daily high records was fairly well communicated on skeptic blogs. (BTW, this trend has also continued for January and February of 2014, with more record low records than record highs.)

via ‘Record temperatures’ placed in context with station history | Watts Up With That?.