Where does one get exact location data?

By comparing location of Everest, K2, Broad Peak on summit post and www.adventurestats.com I found every coordinate is different.

Which one is correct?

Where can one verify the correct coordinates?

These links might be used in the case of Nepal (if the data on the pages is correct (and due to the state of their website it might not be)):
http://www.tourism.gov.np/peaksopedfortrekking.htm

These webpages seem to be broken / incomplete:
http://www.tourism.gov.np/1310peaks.htm
http://www.tourism.gov.np/peaksopenedfo ... vities.htm
http://www.tourism.gov.np/50newpeaks.htm