Nice write up there by Stephen Gandy - good link George. The tick mark lenses are identical to the later 9-bladed F-mount lenses, except for the tick marks. They are definitely not better, just a lot rarer. Fantastic quality, whether they are tick marked or 9-bladed. And the later 6-bladed ones aren't exactly shabby either, the only difference is some of the out of focus characteristics.
From a couple of samples I have, some of the tick mark lenses have a longer rear lip of their aperture ring, which prevent mounting on the Df. Other folks here haven't had that issue with tick mark lenses.
