Slightly Embarrassing Question

Haven’t done that but probably should. I would be FLABBERGASTED to find out that was the cause. It feels very mechanical and very much tied to vehicle speed. Also, when I let off the gas the vibration gets worse, like it’s my driveshaft flopping around. I guess my question is “could I have driven for 15000 miles with the wrong harmonic balancer or would it have been way crazy if I was using an internally-balance balancer if I was supposed to be running an external balance harmonic balancer.