Will anyone notice if I'm off by a year?

When I teach history, I always ask my students to view every "fact" as relative and subject to interpretation.  Inevitably, someone will ask: "Well, what about dates? Those are facts."  But dating and calendar systems vary widely, and may not be consistent across different groups of people. 

I've been thinking about this recently as I struggled with the timeline of my own novel. Monster at the Gate begins a few months before  the plague struck London in the 1660s.  I start the novel on Shrovetuesday in February 1665 (a crazy strange  day before Lent) and end with the Fire of London the following year (September 1666). Two clear beginning and ending dates,  spanning about nineteenth months in total. Easy enough?

NO! As I was writing, I kept running into odd inconsistencies with the historical records I was using (such as Pepys' Diary), trying to double-check details. I kept finding that Tuesdays should have been Sundays, or that Easter had occurred at a different time than I expected.   I knew that historical records would say 1664/1665 or 1665/1666, but I couldn't remember the exact details of how contemporaries kept time.

(MUCH GNASHING OF TEETH!!!!)

Finally,  I sorted it out.  England was still on the Julian Calendar (which had been adjusted for a missing ten days), rather than moving to the Gregorian Calendar used by most of Europe  (it did not reform its calendar until 1752). To make it even more confusing,  the Julian Calendar year starts on March 26, not January 1.  But luckily I found a historic date calculator to help me keep it all straight.

So, my book technically starts on Feb 7 1664, and ends September 3, 1666, and that's still only nineteenth months.  You do the math!

But I'm wondering if it will confuse my readers if they think the book is starting in 1664, when by today's modern calendar, it would actually be 1665. What do you think?