My understanding is that if you play a 'provisional' ball it is only in play if you cannot find the original ball. Once the original ball is found it must be played. Once found, you can declare it unplayable then proceed under the unplayable ball rules to put another ball in play. The provisional, however, is no longer in play.

If the first ball is not found, the second ball 'provisional' is in play. If both balls are not found, then the third ball 'provisional' is in play.

Suggestion: If you hit your ball deep into the woods and suspect that it will be more trouble if it is found... don't specify the next ball as a 'provisional'. It then becomes the ball in play.