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
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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