Calendars - Hey where did those 12 days go??

I'm a musicologist by training (also a conductor or sorts and no, not the train type).  We, in that trade, deal in minutia.  Having never met a footnote I didn't like and having some affinity for physics and inventions, I was always fascinated by time and the attempts to map it and tell it.  WAIT WAIT don't run away, there is a point here.

There has been or was, however, a fair sized battle about telling time and what year was it or is it and based on what calendar..Julien or Gregory, or for that matter, the atomic clock.   I like this little bit from Wikipedia which is actually written by someone who gets it.

Simply when dating events prior to 1752 you have to look and see what calendar was in use and who was using what. Frankly you have to look at stuff past that date as well as nothing happens all at once...it is like global warming, there are early signers on and those late to the party.

Anyway, 12 days is a big jog in history..like waking up in the middle of next week...Happy New Year or not.