And there's also this (and I am speaking of LE agencies-you didn't specify if it's LE, concealed carry class, or range rules):
In the scenario you set out (qualifying) you KNOW you are going to be firing all the rounds. In real life encounters-you will likely NOT be firing-only covering or drawing and then reholstering. Then, you have the cocked revolver to deal with. Even if it's on the 2nd, 3rd, or 5th shot (to align better with your scenario of "after the first shot".)
Heres where I fear I may "step on toes" but this is the no BS answer. As stated above most policy and doctrine on revolvers only acknowledged DA fire in defensive situations. But AFTER the situation has changed (he's down-now have to move to cuffing, or it changed from a deadly force to non-deadly force encounter) the NOW COCKED revolver is a major safety concern. I KNOW that it's a nearly thoughtless and completely natural movement to a real revolver guy or gal to thumb the hammer and pull the trigger and follow it down, BUT tons of negligent discharges have occurred at this stage, in both LE, military and civilian settings. Even by serious gun aficionados. Even with highly trained shooters and instructors. I KNOW that would never happen to you, but it happens, and those folks never thought it would happen to them either.
So I don't think agencies (and maybe instructors even in the CHP classes) are not willing to even acknowledge you may be standing there with a cocked revolver that needs to be made safe, at any stage, on the range (or later, on the street). I certainly wouldn't encourage it or even knowingly allow it as an instructor, although I sometimes shoot SA when shooting recreationally, but that's it.
Not proud of this but I had two NDs in my entire life, and both were with revolvers, and both in my teens before I ever had a DAY of formal firearms training. Fortunately no one was hurt, but because of this I am even more vocal (like how sometimes the most vocal non-smoker is a former smoker).