The Tale of Years chronicles the second and third ages. The Third Age began with the first overthrow of Sauron and taking of the One Ring. It ended more than 3000 years later, with the destruction of the One Ring, and the end of Sauron.
All of the events listed in the Lord of the Rings are in the Third Age years. To convert the years into Shire, you must substract 1600 by the Third Age date. For example: The downfall of Barad-dur, occured in III 3019 but in shire, the date is 1419; 3019 - 1600 = 1419.