I always use the dates given in historical documents unless there is 
an error on the author's part. The reasoning is simple: those who 
create documents create them in their calendar context. Historians 
may inhabit other calendar contexts. If we are to communicate 
successfully with one another now and in the future, we need a point 
of reference that we all recognize. The original document date (or 
time) is such a point.
Adam Smith's baptismal date was June 5, 1723, to those involved in it.

Samuel Bostaph