FH100 Pilot,
reading on from your extract of AC 29.297A - Additional Tests, one sees this text:
A bench test (transmission test rig) is commonly used to demonstrate compliance with this rule. Since this is a test of the capability of the residual oil in the transmission to provide limited lubrication, a critical entry condition for the test should be established. The transmission lubricating oil should be drained while the transmission is operating at maximum normal speed and nominal cruise torque (reacted as appropriate at the main mast and tail rotor output quills).
Whilst I agree with your contention that the language is, of necessity, imprecise, use of the word drained does rather suggest that the colloquially used term 'run dry' is close to the real meaning.
Mars