But following the events of Genesis of the Daleks, the Doctor set back their development one thousand years. It wouldn't be much, but it would have an impact on the previous adventures. We have no real way of telling how many of the previous stories were affected by this.
The problem with the Daleks is that they are time travellers. What is "early" in their time stream and what is "late" is a matter of debate, indeed if the First Doctor's suspicions are correct The Daleks is set many millions of years after The Dalek Invasion of Earth and the devolution happened between these two points. In this timeline presumably they never had the Doctor interfering in their events and so they went off and began their conquest of the galaxy, as the Doctor encounters them, each time their timeline is disrupted further and further until we have no idea what has happened and what has not.
Time is in flux, it is not a straight line, it is a big ball of wibbly-wobbly, timey-wimey stuff that is hard to understand. For all we know The Evil of the Daleks happened fairly early on in their timestreams, all that we can guarentee having happened before it is The Dalek Invasion of Earth, The Chase and Genesis of the Daleks. Therefore there are potentially only three versions that are pure, and if The Daleks is anythign to go by they have been sitting around on a radiation soaked world mutating continuously for millions of years. Generation after generation the Daleks will have become impure.
Potentially only the Genesis models and the Paradigm are "pure" as they are the only ones with the original specifications of Dalek DNA.