Hello again,
The 200k pot may in fact adjust the output zero center point, but that looks like it's just a secondary effect.
As you adjust that pot and the output DC operating point changes, it also changes the current through the two diodes and 22 Ohm series part which changes the voltage drop across that little network, and also causes currents from Q3 to Q4 and from Q5 and Q6 (of the second drawing) to change. The effect would be that the output DC center zero point would change, but more importantly the crossover distortion would get worse or better with the adjustment.
I say this for now mostly because the crossover distortion is a major concern in these amplifiers, whereas the DC center point is only of concern if you need to get the absolute maximum output voltage range and that would only be a concern at maximum volume, and probably still not that much of concern.
A question might be, is the innate output DC zero bias point so far off that it needs an adjustment, or is this just like any other typical bipolar transistor power amplifier that needs to reduce crossover distortion while keeping quiescent current low.
An in-depth analysis would tell us more about both of these functions, but my bet is on the cross over distortion issue, and that stands even if the designer thought the adjustment was going to be for the output DC zero center bias point.
Still, this amplifier does not have a complementary pair output, so that could present a DC zero center bias point issue.
To be sure, we'd have to do a complete analysis for both the DC zero center point bias AND the cross over distortion. Then, see how the adjustment affects both.
What also shifts my opinion toward the crossover distortion issue (without doing an in-depth analysis) is that I always read about people complaining about crossover distortion, while I do not think I have ever read one post about someone complaining that their DC center bias point was way off.