In my studies (such as they were) for Russian history at A level, I was always intrigued to note that
their 'February Revolution' was in March, and their 'October Revolution' was in November, 1917. See
https://www.bl.uk/russian-revolution/articles/timeline-of-the-russian-revolution 
That could very well have confused even Sean Connery, in 'The Hunt for Red October', if such things hadn't been sorted out subsequently.

Or you can be a year out. For example, the Acts of Union of 1707 were in practice two acts, each with its own formal title, one in each parliament. The Scottish act passed first, in January, followed by the final vote in England, in March, and the union began in May - all in the same year. So a (yes, rather pedantic) combined citation might be: "The Acts of 1707 in Scotland and 1706 in England of the Anglo-Scottish Union of 1707".
The point being that the new year was January 1st in Scotland from 1600, but in England remained March 25th until 1752. During that interval (in both senses at once) you had to watch out for the difference. And, if you go poking about in old documents, you still do.