You make a very good point. The booklet is a compilation of lectures that Carroll gave on church history. Carroll died in 1931 before the book was produced, but J. W. Porter brought it out after his death. Further, even the full title denies that Carroll thought that John the Baptist started the church -- The Trail of Blood, Following the Christians Down through the Centuries. The History of Baptist Churches from the Time of Christ, Their Founder, to the Present Day. I further believe there is merit in remembering that faithful Christians (whether Baptist or not) who simply tried to follow the principles of the Bible left a "trail of blood" created by their persecutors who held the power of state. Foxe's Book of Martyrs and van Braght's Martyr's Mirror demonstrate this in much greater detail.Many make ToB into something it isn't and has never been. ToB is a compilation of notes and the charts from Carroll's lectures he gave in various churches. It is not a comprehensive work.
I believe The Trail of Blood errs in identifying some groups as Baptist when they cannot be convincingly demonstrated as much. However, The Trail of Blood has become the "whipping boy" of those who deny the premise of Baptists (or baptistic churches) in all ages from the time of the New Testament. It is much easier to critique a little booklet of 50 or so pages than to take on critiquing Joseph Ivimey's 4-volume A History of the English Baptists, the almost 600-page Baptist History: From the Foundations of the Christian Church to the Close of the Eighteenth Century, by John Mockett Cramp, President of Acadia College, Wolfville, Nova Scotia, or the two-volume A History of the Baptists, by John Tyler Christian, Professor of Church History at the Baptist Bible Institute, New Orleans, Louisiana (later renamed the New Orleans Baptist Theological Seminary).
The position of Carroll is not specifically Landmark, as some believe, but has been held by any number of Baptists in various times and places, such as non-Landmarkers R. B. C. Howell and Charles Spurgeon.
Charles Haddon Spurgeon said:We believe that the Baptists are the original Christians. We did not commence our existence at the reformation, we were reformers before Luther and Calvin were born; we never came from the Church of Rome, for we were never in it, but we have an unbroken line up to the apostles themselves. We have always existed from the days of Christ, and our principles, sometimes veiled and forgotten, like a river which may travel under ground for a little season, have always had honest and holy adherents. Metropolitan Tabernacle Pulpit (Volume 7, London: Passmore & Alabaster, 1861, page 225).