What is confirmed by the fact that the Lord has not yet begun to take vengeance?
Revelation 6:10 (ESV)
10They cried out with a loud voice, “O Sovereign Lord, holy and true, how long before you will judge and avenge our blood on those who dwell on the earth?”
That the Lord has not yet begun to take vengeance would confirm that the second, third, and fourth horses have not yet gone out when John sees this vision.
10 They cried out with a loud voice, “O Sovereign Lord, holy and true, how long before you will judge and avenge our blood on those who dwell on the earth?”