Couple of points. Yes, if you are not sure the ball is in the hazard, (you do not have what is called "known or virtual certainty or KVC" you can not assume the ball is in the hazard. If you don't have KVC, DECLARE a provisional and replay your stroke in case you can not the original ball.
If you go forward and look for your original ball, you can not go back and play a provisional. It's too late. The whole idea for allowing a provisional is to save time, so you must play it before you go forward to search for your original ball..
You are correct, if you are not sure the ball is in the hazard, you can not drop under the hazard rule. One thing though, if you do drop it in this case, you can under Rule 20-6, correct this mistake and pick up your incorrectly dropped ball before you play a stroke with it. So in other words, when you dropped the ball, if someone saw your original, you could pick up your dropped ball and proceed correctly with your original ball,.
Also, one clarification on the ruling for what your did, If you dropped and played by the hazard, instead of replaying your stroke, you would have not only played from a wrong place, but have been deemed to have committed a Serious Breach because you gained a significant advantage by playing up by the hazard instead of back where you originally played the stroke. In this case, you would have to abandon the ball you played incorrectly from the hazard, and correctly play under the lost ball rule. This means go back to the tee. You would be hitting 5 from the tee.
Hope I haven't confused you too much.. This rule comes up a lot here and is often misunderstood.
Edited by Dormie1360 - 1/27/14 at 11:19am