the calendar change only occurred on that date in Britain, so if you are dealing with any foreign documents it may be worth checking when their calendar change happened (there may even be some countries still using the old calendar) Russia for instance was still using the old calendar in the early 20th century..
The date differences can lead to some strange things, for instance I have a stamp collection which contains some postcards that appear to have arrived before they were sent, they only had to travel 3 or 4 miles but crossed a border between countries using different calendars so the despatch postmarks are several days after the arrival ones, mail travelling the opposite direction appeared to have taken an excessive time to arrive.
I wonder if people migrating from one country to another would have adjusted their birthdates to account for the calendar difference? could present some real problems to those of us with overseas ancestry.
Jon