Chronological Considerations

In response to last week’s post about where “Chips” gets his information about chronology for the “On This Day” posts, twitter user @spacefall said:

I once made a rough chart of full & partial chronologies from 1932 – 2013. It looks like this:

Spacefall's chronology chart
Chart by Spacefall and used by permission – click to see full-size

— spacefall (@spacefall) May 12, 2016

This week, let’s talk about chronology. What are your favorite sources for establishing the chronology that is sometimes a bit muddled in the Good Doctor’s writing? Have you tried to write your own chronology of the stories? Why is Watson sometimes so clear about dates, other times very vague, and occasionally downright perplexing?