Every show holds back seats, since they need to ensure that if their premium seats sell, they can add more.. so it is just a game as to whether they will have enough to sell at premium prices, or whether you will benefit from them having held back more than they can sell at that price.
If they do add them, they will usually only be regular price, in the same area as the other premiums, and not benefit from online discounts (but could show up at TKTS). So it is a dice roll, and could cost you more...
The best thing to do, if that is the only time you can go, is buy the best seats you can now. And if more amazing seats open up, call Telecharge and ask them to move you to those newer seats. That said, it will not be a plain old transfer. They will refund your old order and create a new one. Typically, it has to be for seats the same price or higher. If the show sells worse, and they add more seats at cheaper prices, then I'm not sure what happens. Perhaps you can move closer, but not at a cheaper rate?! Never encountered that one...