I went through the exact same mental torture with my "vessel load" date changing at least 3 times. Also, my car was in "production" status for weeks (likely due to the holidays and perhaps issues being discovered during quality control), so it seemed like an eternity before I got my VIN. It was quite frustrating to keep seeing those dates get pushed out.The "on boat" date has also changed twice from 6/21 to 6/25, and then again today I was told it changed from 6/25 to 7/4. So, right now my trends aren't making me too happy.
My dealer has been doing the same, every couple of weeks usually, and in certain circumstances several times over a few days.There is no standard. It just depends on the dealer you get. Mine kept me updated every couple of weeks, and sometimes more frequently if there was new information to be provided.