You can contact DD customer service @ service@danieldefense.com and they can tell you when it was made with a serial number check.
As far as value goes, the entire AR market is in Trump Slump 2.0, so it's possible about $1500 to $1750 in condition you mentioned. If you're looking to sell quick, then under $1500 of course.
DD has been consistently good so quality over time is level and great IMO.