There is a message from the ISD team at NCDC on the ISD FTP server about a problem with their merging process:
NCDC has identified a problem with merged ISD data. Under certain circumstances station merging is not taking place when it should, resulting in unsorted, non-merged output. This problem may be found in files on this FTP server from 2005-present.
We are working to correct this issue and we apologize for any inconvenience this may cause.
This may have affected v220.127.116.112p and we are investigating. We will wait until this issue is resolved before finalising this update and creating v18.104.22.1682f.
Please let us know if you find anything untoward in the data.