This guitar came up on eBay in February 2011 and sold for $2,900. Very nice Dan Armstrong in overall excellent condition. Also, note that the serial number is AD421AD, which was a production anomaly on someone's part in adding the extra letters. Came with RB and CB pickups.
This one came up for sale in April 2015 and quickly sold for $2,800, which seems to be a decent price given the better pickup selection (RT, CB, RB) and intact case. Here's what the seller had to say...
"Up for sale is a vintage Ampeg Dan Armstrong guitar, circa 1969 judging by the early serial number. This one is in very nice original condition and can easily be considered collector quality. I don't think this one's seen a lot of use over the years, as the pickguard is still intact with no cracks around the input jack or switch as you often find. There is one very minor chip in the edge of the pickguard, but you really have to be close up to see it. All electronics work as they should, although the switch is a little soft when going from side to side, which is typical of the OEM switches. Looking from the back, everything looks to be original although I haven't taken off the pickguard to check pot codes or anything like that. Again, it all looks untouched and when you look at the screw holes in the lucite it's all pristine so I don't think the pickguard's ever been off. Comes with three pickups - Country Bass (CB), Rock Treble (RT) and Rock Bass (RB). The latter pickup is extremely rare and sounds great. The CB and RB are apparently original to the guitar (color and letter stamping are identical) and were the two pickups I received when I bought it. The RT I sourced later, but is in the same excellent condition so it matches up very well."
"Frets, neck and fingerboard are all in excellent condition - frets are almost in original condition and only the first two show any signs of wear. Headstock and top of neck seem to have had some clear overspray at some point in the past to cover up a few small scuffs at the very top of the headstock, but hard to say, could be factory too. Back of neck is in great condition, no wear and no dings that I can feel. Regardless, the headstock edges are all still pretty crisp and consistent with light use over the years. I have not had the truss rod cover off, and since the neck looks to be virtually flat the entire length there's really been no reason to open anything up."
"Also included is the original OEM Dan Armstrong case with both keys. This is one of the nicer DA cases I've seen - very minor scuffs on the outside and really excellent condition on the inside (Ess & Ess sticker is intact, accessory lid closes nicely and latch works). On the outside of the case, the original handle and 3 latches work very nicely. No musty odor or cigarette smell either that I can tell. Again very hard to find OEM cases in this kind of shape. The guitar also comes with an extra bridge saddle, which looks to be the medium height one that nobody ever uses."
"Please let me know if you have any questions that I can answer. Guitar will ship via UPS (signature required) in a new ULINE guitar box with plenty of bubble wrap and foam peanuts to ensure safe arrival. SORRY, NO INTERNATIONAL SALES, domestic only."