"There is no proof that Witchcraft has any historical basis prior to the last 50 years."

FALSE.

This is because of the persecution of Witches and the fact that many people could not write long ago. However, a few documents have survived in private hands, and there are, of course, the documents held by the church which seem to point to the continuation of the Craft. (After all, why persecute something you do not believe exists?)
The absence of a long written 'pedigree' does not invalidate a belief system.