As Andy said, you need a special meter to measure low resistances accurately. I use a GW Instek GOM-802.

Terminal resistances (AB, BC, AC) will be about twice the numbers given in the OP, which are coil resistances. Measuring coil resistance is done from each terminal, A, B, or C, to the collector ring on the side of the stator away from the terminals. Measuring terminal resistance is obviously more convenient, and is fully acceptable, since that's what the ESC "sees". (You can also use the terminal resistances and some algebra to solve for the coil resistances.)

Expect a good 17.5 to be in the low 40 milliohm range for terminal resistances. As Andy and Roeloff stated, 19 milliohms for each coil (38 for terminals) is suspect.

You'll also need to know what temperature the stator is at, as copper resistance has a large (+0.39% per degree C) temperature coefficient. It is customary to report the result corrected back to what it would be at some reference temperature, usually 20 or 25 degrees C (I use 25C).