If you're assembling the motor for the first time and just now installing the cam, there will be no compression or overlap or anything else on #1. The piston will just be at TDC with no reference points at all because the cam is not in the block yet to make reference points to overlap or compression. The crank gear dot will be at noon. With #1 piston at TDC, that's when you intall the cam with the cam gear dot at 6 PM. Not until then will you have overlap or compression to refer to.

What they left out of their explanation is that there is no chain on the cam sprocket at this time. They are saying to position the cam gear at 6 PM, then rotate the crank until the crank gear is at noon. Install the chain around both sprockets and nail the cam sprocket to the cam.