I contacted Steve while trying to figure out the origin of this
calendar, and he was both shocked and pleasantly surprised to hear that
this material was still being read and that it had ended up in some Star
Trek novels. He gave me permission to post this Klingon History
document here.
I took what Christopher had given in his Calendar Notes, and did ALOT
of math (and I mean ALOT), made a few tweaks to the small details, and
learned an insane amount about Excel so I could create a calculator to
convert dates between the Earth and Klingon calendars. Then I analyzed
all the mentions of Klingon dates I could find in episodes, novels, and
comics.
Then there is the other Klingon dating system, which was also mentioned
in an episode and several novels. This seems to be a totally different
way of reckoning the Klingon year. Each example of its use seems to be
in relation to logs given by members of the Klingon Defense Force, and
as such I theorize it is similar to the Stardate system used by
Starfleet as opposed to the Gregorian calendar used for common Earth
dates. I've analyzed it as much as I could.
Add to all this data a fair amount of extrapolations I've made
concerning holidays, birth dates, and the Klingon military, and you'll
see everything I've been able to figure out about the Klingon Calendar.