"Good news", with the number of 200 or 300 years old trees that are currently dying, we will be able to check all records when we'll have them cut down.
- There are many research available that used tree rings to determine past draughts. And yes there were much worse and prolonging ones. Some research goes as far back as a millennia.
- Yo do not need to kill a tree to get ring information. A drill is sufficient.
This may be useful too http://drought.memphis.edu/OWDA/