I had a couple of those that were stocked in walnut and were stamped the same way. The stocks were very dark and slightly oversized. They weren't completely finished either. Both of those rifles also had an aluminum tag on the front swivel with the same number and the name of an ordnance repair depot. Other than that, nothing else. The number on the stock didn't match anything and were to high to be rack numbers. They both had the same AA prefix and 5 digit numbers that you describe.
If anyone actually knows the significance of these markings, I would like to know for sure as well.