Your lab is misleading you, to put it mildly. If you give me a grey negative, I can print that grey anywhere from pure white to pure black, so looking at the print tells you very little, especially for photos of a grey card.(posted 9271 days ago)If you have a spotmeter, you can use it as a densitometer. Instructions are in "Beyond the Zone System" by Phil Davis, or quite possibly in this forum somewhere.
You can get less precise results without a densitometer, but in any case you certainly must look at the negs, not the print.