I would recommend reading any notes or preface to a book. These often explain the methodology behind dates, translations, and names. As a general rule most Western books will be using the Gregorian calendar. In societies where the Julian calendar was used (such as Russia), writers will let you know how they are dating. Western writers typically will put the Gregorian calendar date with the Julian date in parenthesis. They may write "O.S" for "Old Style". So the February revolution my be written as starting March 8th, 1917(O.S. March 23, 1917). In my go-to book on Russian history Russia and the Soviet Union by John Thompson, he outlines in his preface this mentality. Since he is catering to a Western audience, he uses a western dating system.