Please note: this is helpful, and works well, as long as you are not using Apigee X or hybrid. In Apigee X & hybrid, all the KVM are encrypted, so if you drop the private. prefix, you will get nothing loaded into your variables.
In those cases you can use an AssignMessage / AssignVariable for the same purpose. Just attach the policy immediately following the KVM policy. Something like this:
<AssignMessage name="AM-Diagnostics">
<AssignVariable>
<Name>observed1</Name>
<Ref>private.variable-presumably-set-by-kvm-get</Ref>
</AssignVariable>
<AssignVariable>
<Name>observed2</Name>
<Ref>private.another-private-variable</Ref>
</AssignVariable>
</AssignMessage>