I think what Dale said makes sense too...
What engine does your car have? 325 HP, 360 HP, 375 HP?
I think documentation is nice, but if the original engine is a 325 HP, then less important (IMO).
Documentation is always nice, but its moree important for "Proving" the cars heritage (SS or clone, 360 HP, etc...)... The more rare the options, the more desirable the documentation will be...
With the 66, the VIN proves its an SS, and if the car has mostly standard equipment (and mainly the engine), then if probably will not make too much difference.
I think the "big dogs" will not only want documentation, but they will want a car thats fully done, at least for maximum dollar value... If the car is not really nice condition, then the documentation isn't worth as much...
Of course, its also worth more to some people than others, and some buyers might only be looking for documented cars...
I was thinking that maybe the car was from Fremont (because of your location). But you mentioned Baltimore... I think Fremont cars rarely had the builtsheet...
Where are you (Sacramento area)? I live in Elk Grove and have a few 66 Chevelles...