Unit test fails because TimeZoneInfo does not use the correct DST transitions.

gistfile1.cs

/// <summary>
/// Is the specified datetime DST?
/// </summary>
[TestMethod]
public void DST_Started_On_April_27_1980()
{
    var ts = new DateTime(1980, 4, 15, 12, 0, 0);

    var isDst = Utils.EasternTimeZone.IsDaylightSavingTime(ts);

    Assert.IsFalse(isDst);
}

internal static readonly TimeZoneInfo EasternTimeZone = TimeZoneInfo.FindSystemTimeZoneById("Eastern Standard Time");