On an engine dyno, the throttle goes to wide open and the motor is allowed to stabilize against the load before the “pull” is started.
Most pulls are done from low to high rpm.
As long as the pull starts at an rpm lower than where the motor makes peak torque, you’ll get a good picture of the shape of the power curve, and where the peak occurs.

With a chassis dyno that has these same capabilities........being able to hold the load against the absorber to get things stabilized....... then starting the pull from that point....... the beginning of the pull would always be whatever the converter stall speed was.
That would always be the lowest rpm where output was recorded(if the test was conducted in that manner).
So if you had a 5000 stall converter, there wouldn’t be any data below that point.

Again, if the engines peak tq was well below that rpm...... that would still be the point on the sheet where the highest tq was observed...... and would in no way reflect where or what the engines peak tq output really was.