Perhaps abgd, the plastic collet is missing from your throttle lock. In this case, you'll know, as there'll be no locking whatever. If there's some, it's all there, but worn.
On the topic of throttles of that type, or indeed any push pull engine control cable, there should be (and you want to assure) "bounce" at the maximum power side of each engine control. The control can be felt to hit the engine end stop before it bottoms out on the panel. That way you know that you're getting full travel out of that control. If it bottoms out on the panel, you cannot be sure - it needs rerigging. Every now and then, give the throttle a heart tug in the "closed" direction. occasionally cables break, and you'd rather find that on the ground. I know two pilots who had the throttle come right out in their hand, cable and all, when they closed it in flight.
I am definitely not a fan of vernier throttles. Fine for mixture, and prop, but throttle must be able to be closed quickly with no obstruction. I'm not aware of any aircraft in which a vernier throttle was original equipment.