Well, I don't think you will ever get your exposures correct by shooting with one camera, then simply using that as a measure for another camera. You will have to experiment with each camera, lens, exposure meter, film, and development.

In other words, 35mm TMax 100 shot in your Nikon will not help you much in figuring your exposures for 120 TMax 100 shot in your Rolleiflex or your 4X5 TMax 100 shot in your Crown Graflex....and from my experience, lab processing "usually" will not be nearly as consistent and proper as if you took the time to experiment and adjust your development times doing the processing your self.

Dust? Blame it on the lab.

As for your exposures...it's hard to tell without the negative in front of me.