If you want to keep abreast of the expected delivery date, I would advise weekly calls to the dealer and ask him to check the system whilst you are on the phone - and if you don't believe that he is checking, turn up in person and watch over his shoulder as he checks
In my case there didn't seem to be any trigger where they called me except for when the car arrived in port in Southampton. But every dealer is different and I called a lot so perhaps other dealers are better are keeping you informed. Start of actual production + 5/6 weeks still seems a good rule of thumb.
Good to see lead times coming down finally