If you found and applied all the hints, there's no need to repeat -- the correct year is unambiguous. The correct day may be a bit fuzzier, but follows the common-sense interpretation of the hints.
I think that's misleading, and it would have helped me not to have had that advice.
There are a few criteria you can glean from the calendar itself. Apply those to find a list of suitable years. Depending on the tool you use, and whether you find one particular subtle clue, your list may have 14 years, or 10, or 8, or 5, or maybe some other number.
It's "unique" in the sense that if you find the more subtle clue, then interpret your list of years according to another clue in a particular way (interpreting "**" to mean a year not a person, and "*******" in a way that applies to years, not people, and counting from the right end), then you'll have a unique year.
IMO the day of the month interpretation is "common sense" only if you don't think about what the clues actually say, and that's not what I think of as "common sense". You'd have to believe someone circled the previous day on the calendar when the event in question occurred, then wrote "tomorrow" to mean "today" or something. It doesn't work. Just take the word "tomorrow" as meaning "increment the date", and don't try to use common sense about the wording.
From the comments so far, most people who have found this one easy didn't try to interpret all the clues. It's easy when you ignore the clues and just treat it as a test of your google/wikipedia ability. Just narrow it down to the list of 14 or 10 or whatever you come up with, and look at the wikipedia year-summary pages for each of those years. As long as you've applied the most obvious clue correctly, you'll get it.
Also, when you do this search on wikipedia, look at all categories on each year summary page. The "common sense" interpretation of some of the clues might steer you away from events for which the date wouldn't be known until it happened, and that would be steering you wrong. You have to imagine that when this event occurred, someone circled the *previous* day on the calendar, for some reason.