If a decedent wrote a holographic will dated 2006, but then changed the will with another holographic will in 2012, which holographic will is valid?

The latest document would revoke the first one as to clauses that are identical. So, for example, in the 2006 will if it says the decedent names Bob as executor and the 2012 will names Jim then Jim would be the executor. However, if the 2006 will names Bob and the 2012 will is silent as to executor then I would argue that Bob would be executor even though other terms of the 2006 will may not be valid. In short, it could be a combination of the two documents.  -John