Raid, I believe what radiocemetery was referring to is somewhat different than mounting or un-mounting Geiss C4 lenses properly. The C4 uses a rangefinder assembly that screws down onto the die-cast chassis, and if these screws loosen, the whole rangefinder unit (including the knurled adjustment wheel that meshes with the focusing ring around the lens) can acquire some "slop". The result of this is that the knurled wheel and the focus ring can skip teeth, causing the rangefinder to get out of adjustment.
With the Geiss modified C4, this problem still remains. However, as you have stated, getting the lenses properly mounted is something else to be aware of. Fortunately, this is a simple affair. Just be sure that the distance scale on the adjustment wheel is lined up with the infinity mark, and that the lens to be mounted is also set for infinity. Now, swing up the small lever on the front of the camera body, seat the lens in place, and swing the lever down to lock the lens in place. For the standard 50mm Cintar, you don't have a distance scale on the lens to refer to. To set this lens to infinity, you need to be sure that two small red marks on the back of the lens are lined up.
I do wonder if you had the lens mounted properly, since your final photo shows the closest portion of your daughter's arm to be much sharper than the rest of the photograph. However, if you were using slow speeds and your daughter was moving, any analysis of sharpness is basically worthless. I do maintain that the Cintar should have performed better in this situation. The lightly hazed Leitz Summar (a lens commonly avoided due to concerns about low performance) that I've been shooting lately produces better results than these, and it's also being used wide open at f2.0. I'm fully aware that sharpness doesn't define whether a photograph is good or bad, and you don't have to look very far for solid evidence of this fact (just pick up a book about Robert Frank or Robert Capa photographs from the 1940's or 1950's). Furthermore, I do understand that "good" can be a subjective term relying solely on one's opinion. However, I feel that in this particular situation, sharper photographs would have actually improved the final result.