Be careful of the last build by dates, people saying agh yes but car 3 was 'built' after car 5 was 'built'.... they normally went down the line sequential in there respective series, the dates we refer to at Gaydon are not build dates, they are dispatch dates, the day the cars made it through to the dispatch department/compound..
It is still the same today, the official last of line cars that get pictured are indeed the last vehicle to come of the line, however by dispatch date, there will almost certainly be a pile of chassis numbers/cars that go into dispatch after the last official built went through.
For me, I always personally use the chassis number series as the master not the dates given by Gaydon. The dispatch dates when looked at in big lots, do go some way to giving you a good guess of actual build.
There are usually two dates in the dispatch register, one for when production passed it to sales and a second when it was dispatched out to the distributer. As said, vehicles were not built in chassis number order but in Build order which was presumably to even out the build content on the production line . Some vehicles will have offline build content after it leaves the main line which can hold it up before being passed to sales . When I worked there there was a Ninety that had a slight bump and was held back for about a week whilst the panel was changed before being passed to sales . One of my S3 LR's was one of 400 built without steering locks due to a shortage so they were parked outside and finished off when parts became available . This means there is no certainty by chassis number as to when it was finally finished and passed to sales and then to dispatch. I agree dispatch date can mean anything , but I think the date into sales is more relevant.