Really??? Both my '69 & '71 shop manuals refer to DSO as Domestic Special Order(North America), which is what I've always heard... In later publications('86 Shop Manual), it's refereed to as District Sales Office, so I suppose it's meaning varies by era and who one asks... There is also a Foreign Special Order, but since I've never seen one, I don't know if it's called out as FSO on the data tag/sticker...
Not a special order car. Could be a dealer ordered car instead of just a unit for dealer stock. Maybe ordered it in for a customer, but nothing special about the order.
Every Ford vehicle produced will at least have a two digit DSO... Here's the DSO, engine & assembly plant list for 1971... Note these codes can vary so don't take this as gospel for every year...
First time I've seen it called "Domestic Special Order", you would think that every car would have been special order, since they all have a DSO? Here's a link to more info, it's been on the net since 1996: http://home.comcast.net/~petebre/maverick/decode/index.html
I believe the DSO should be thought of as District/Special Order or D/SO... Or District in all cases and Special Order only if it has a six digit number...