Nobody publishes a real minimum safe flow for their pumps. They will work safely at much lower flow rates than you would expect. I had to do the testing myself about 25 years ago because I could not get an answer. Floating stack impeller designs like Goulds have very little friction in the pump end, and need very little water flow to stay cool. As long as the motor amps are decreased when the flow is restricted, the motor has been de-rated enough that it could safely pump hot water, so again it takes very little cool water to operate safely.
Again the bare minimum flow for a 2HP or smaller is 2/10's of a GPM. This is why the minimum built into the CSV is 1 GPM, which is 5 times more flow than needed to keep the pump cool. 3HP and 5 HP motors can stay cool down to about 1 GPM, which is why there is a 3-5 GPM minimum on those sizes of CSV's.
Pump manufacturers don't want you to know the minimum cooling flows are so low for normal pumps. That is because the VFD's they are trying to sell you do not de-rate the motor and still requires a full 0.5 feet per second flow to cool the motor. They just don't want you to know that a CSV is much better for the pump and can safely work at lower flow rates than VFD's.