On track my Vauxhall its not a build date, the first date you get just tell you the date it was given a build slot, but not when it is.
Mine was given a build slot in September, but the Car arrival week has moved three times.
Dealer first guess was late November, 10 days later when the he told me December 24th, then I found http://www.trackmyvauxhall.co.uk/
and called him for a number and saw 28th Dec, then 4th Jan now 18th Jan.
Honestly if it goes into February I'll be off to http://www.automaticcarsltd.co.uk for a low mileage Nissan QQ.
Gave back the company BMW 520, sold the old family Pug 307 for 100% more than dealer offered and now driving 13 year old Micra, the neighbours are passing are the hat around!