Can you really think it correct for airline crews to go out and test the equivalent of the "stalling speed" without having a good idea of what that speed should be, depsite it being presented in a table in the schedule, and still flying (IIRC) some 15K+ below it wondering when things might start to happen
No, it's not.
I do these tests on a regular basis. They are done at a minimum of 12,000 feet, and we calculate the shaker speed beforehand. We begin the deceleration about 40 knots above target speed, and we cannot trim nose up below about 25 knots above target speed. That way there is a big pitch-down moment as soon as we relax a little.....