I think the point here is that the OP is using days cruised as a measurement, this is incorrect. Each cruise garners a number of points, based on number of days and a number of other factors such as whether you are in a Haven Suite etc. At the end of the cruise you are awarded the points for that cruise. So the question is not when you achieved 150 days but did you have 150 points after the second portion of the cruise, if you didn't then you won't become Sapphire until after the cruise were you are awarded enough points to take you over 150.
Example. My wife and I achieved Sapphire status after our last cruise. We had amassed 137 points each from our previous cruises, on our cruise docs our status was indicated as Platinum, we embarked on a 10 day cruise but we received 20 points each at the end of the cruise because we'd booked the cruise as an insider offer. We were awarded the 20 points a day after our cruise had ended and we were then officially Sapphire.
My point being status is based on points, these points are only credited at the end of a cruise. If you hadn't been awarded 150 points BEFORE the third part of your trip then you were still Platinum.
I would also add that the additional benefits of being Sapphire over Platinum are minimal so you must really want that dinner with the officers pretty bad to raise this as an issue.