Verify existing torque on tightened bolt using a torque wrench
This is deceptively hard to test.  

When torque is specified for a fastener, it's really the torque that should be applied when the fastener is installed.  

Your test, which I believe is called a "first movement test" - creeping up on the torque until the fastener moves - tests how much torque it takes to make it tighter right now.  You might naturally assume that it will first move when you first exceed the torque applied when it was installed.  However that's not generally true for a number of reasons - the deformation of the parts upon installation, adhesion developing on the threads (corrosion or otherwise), the effect of static versus dynamic friction, etc. etc.