The big carriers tend to drop their rates about 90-60 days out, it also depends on the passenger load at the time, if 90 days out the flights are 90% full, they won't drop the fare because they don't need to. If it's 10% booked, they'll have a sale for sure! Also, sale fares are like room codes at Disney resort. They only allow a certain number of seats to be sold at the sale price, once they are gone on a particular flight, the fare for that flight goes up, even if the other flights stay down because they still have sale seats left.
BTW, $210 isn't bad from Dallas, really. If you need specific flight times, you may just want to book it now to get the flights you need, rather than take the chance that the sale fare won't be available.