I received a sample of 3/4 inch solid BC from a supplier. It is very nice however when I connect the tongue and groove, there is a noticeable movement (i.e. not a tight fit). Would this be a problem for a nail down installation ( such as floor popping)? Also, the thickness of the planks are 0.71 inches as measured with a digital caliper. I'm not worried about this except for the interface to a 0.75 inch built in air vent. Are thicknesses and tongue and groove profiles not standard in the flooring industry?

Thanks

Only with NOFMA member mills in the USA and Canada has it's own standards. Even some very good mills in the USA have different T&G profiles on the same type of material. If there is some "slop" in the T&G, you will have problems with the flooring moving up and down and not being able to sand it flush. The wood fit should be snug.