You are not allowed to play a provisional ball for a ball that might be unplayable, therefore when you dropped and played another ball, that ball became the ball in play under the stroke and distance option (Rule 28a). When you holed your next stroke your score for the hole was four.
If you thought that your ball might have been lost outside a water hazard or out of bounds, you were entitled to play a provisional ball. However, you had to tell your fellow-competitor or opponent before proceeding. If you failed to do so and played another ball, that ball became the ball in play under penalty of stroke and distance. The original ball was lost. (See Rule 27-2a). Your score for the hole would have been four.
If you had proceeded correctly under the provisional ball rule, (Rule 27-2), and the original ball was found before the provisional ball was picked out of the hole, then you were obligated to complete the hole with the original ball.
Several Decisions relating to this question: Dec. 27-2a/2 and Dec. 27-2b/2