411A,
does that mean that SAS and DLC ( & YD) remained active (or could remain if so commanded) after AP was disconnected as for instance during a manual approach?
Yes, SAS (yaw damping and turn co-ordination) was a full time operation, either manual or auto flight.
DLC was also full time, either manual or autoflight, and was initiated when the flap handle passed the 30 degree position.
... reading some of these messages it appears implied that DLC was unique to the TriStar
Correct, unique to the TriStar amongst civil jet transports.
Also unique was the all moving tailplane for pitch control.
A delight to fly.
Having said this, these airplanes are definitely getting old, and consume considerable man-hours to keep 'em going.
Having Lockheed and RR factory trained folks certainly helps.