So the answer is that you believe it's the same - "run two crews" is the same as "run two shifts". I grew up near cities that had vehicle subassembly plants (Delco, Warner Gear, etc.) and the people working called shifts "tricks", as in "I worked first trick for three months, but now I'm third trick". Third shift could have also been a maintenance shift - or cleaning up / setting up for the next day's first shift. When the plants ran 3 shifts, that is.