The way I recall hearing it, the stock blanks were stamped with some type of acceptance stamp when first received. After being finished into the completed stock the first stamp, of course, has been lost. The completed stock is then stamped with the DAS. I don't believe the DAS is an indication that a "completed rifle" has been "accepted", only that the stock has been.
Joe,
The DAS acceptance mark means the whole rifle has been accepted as a unit on that rifle. It's the last mark applied by the Ordnance inspector indicating it's now government property.