You asked "Are they half way or almost done or 3/4 done??"
To get a more definitive answer, you might try asking a Shapell employee. Perhaps you might even consider stopping in the Astoria sales center?
Shapell is not a public company, and they build to demand. They slow building releases when demand is slow and release more rapidly when demand is high. As far as duration, you will find that the early Gale Ranch homes were built in the mid-1990's. Say 16-17 years ago. I don't think there is 16-17 years of land left to build on. The school district is so very, very sought after that demand is (I believe) stronger than it was in the 1990's. One thing that Shapell is doing to stretch it out as long as possible is making the parcel sizes (lots) smaller and smaller. In the model center they have phase maps that show the planned developments and they show anticipated parcel sizes for the new development.
In case you haven't guessed, I have represented several new home buyers in Gale Ranch. I have some copies of phase maps I was provided at the sales center. But, as always, plans are subject to change. So if you want to stay on top of it, check in with the builder from time to time.