While you can buy a policy before you own the property, if the policy is triggered, you cannot collect unless you own the property during the coverage period.
There are many ways a TownScore or StateScore can drop. For example, tax burden, debt burden, and crime would each have to rise by less than 1% point and school performance decline by 5 percent for TownScore to drop by 60 points. Smaller Score drops are more likely to happen than big drops.