Not all MX trucks come to the eastern shore by boat. Some do some don't.
Now about Insight, it was prettry accurate for me unless something odd happend. I think the reason it pushes the date back is just a precaution on there part incase they can't get a 18wheeler to deliver it. Depending on where on the lot it sits, it might be a while for them to get to it while your truck sits at port.
My delivery date started getting pushed back but it ended up, the truck showed up at the dealer 1 day after the original scheduled date (One week early from the latest scheduled date). I was told that the my truck ended up being on the right part of the storage area, not in the rear where they might have to move a few hundred vehicles to get to it.
BTW, I ordered 1st week of September and it was at the dealer by the end of October. And it did come on a slow boat from MX to the Port of Baltimore.