Gear Pump versus Variable Displacement Piston Pump
The 206A/B, like the 505 use a gear pump. The 206L, 407, 429, and 412 use variable displacement piston pumps.
Internal leakage in gear pumps prevents them from generating any significant pressure at low RPM. This is not the case with variable displacement piston pumps.
Therefore no issue turning a 505 rotor backwards slowly.