David — Here in the Western U.S. we most often will map out the areas to be reclaimed and then devise an approximate greensmix that gets us close to the behavior of the old underlying greens profile. That spec is used to blend a new greensmix. Rarely can we rely on simply using what's underneath the areas to be reclaimed.
The reason we typically install "new" greensmix is that some areas have been lost for 10 years, while others may have been lots 50 years earlier. Topdressing, care, root depth and all sorts of variables make it a lost cause — usually. Even if you probed and tested every 5 feet, you would never be sure. It's simply going to be wildly different at the fronts vs. the edges vs. the corners at the back. Once we have good mapping and a plan of how the new surface areas fit in to the surrounds, we then excavate the areas to be expanded.
If there is drainage, we retrofit connections in the new areas. If there is no drainage (pipes), then we make sure the new areas have some sort of outfall, or that they will percolate and move into the green area to be preserved. That part is often an allowance in our work. This way we take each area, and each green, separately. Some get more work than others.
Then we install the new mix. Sometimes we re-use the excavated materials as it has sands and soils (and organics) that we test as suitable, along with new sand, peat, etc. A blend is created, regardless of whether we use old materials.
Once the new mix is placed, we then finish, seed/sod. In a few instances we have stockpiled sod on plastic sheets, then re-install it. I did this in Anchorage last year when we re-built a green that had settled due to the earthquake. We stripped about 2,000 sf of sod and kept it for 3 days. Then re-laid it. Oh, and it rained continually, which it does in Anchorage...a lot.
It boils down to a team effort of your golf architect, super and whoever is doing the work. I would guess that 90% of the expansion work we have done is bid or negotiated to a qualified golf shaper/builder. But, I have never seen these projects without a very hands-on super involved. Maybe only a few times, and it was not ideal.
Tom. D. makes a great point about excessive topdressing. You don't want to have a lumpy expansion area where nothing looks right. That is probably the most common mistake I've seen where clubs have tried to go about this in-house. They go down the "light lifting" path, and — frankly — it ends up looking like they did work — but poorly. I've seen some great work done by Tom D., Gil and C&C at some really famous clubs. The common denominator is that Tom D., Gil and C&C were all there overseeing it.