I think you guys need to clear up with yourself if bitcoins are an asset or a currency. If they're a currency, then theoretical not bitcoins are stolen. You could ask, how many are mismanaged.....
So you would assert that dollars, which is a currency, cannot be stolen?
None have been stolen. All coins were spent by everyone who controls the unspent outputs using the private key of the bitcoin address where the coins are.
By that logic, no cars have been stolen. All cars are driven by someone that controls the car using the steering wheel, engine, and brakes.