infrared marks don't seem to be as common as they once were -- i found one on my 50-year-old summicron 50, but not on the rolleicord or yshicaflex.

Where it is found it is usually a titch to the right of the zero point so that when you move to it, yu actually focus a bit closer to allow for the different focus point of the infrared light. Perhaps lenses are better correctd and the mark is no longer needed? Or only needed for longer lenses where the depth of field is more critical?

I'd do a test, shoot half a roll focusing dead on, and half a roll adjusting each shot 1 mm to the right (closer) on the focusing dial and see what comes out.