I would guess that the people tasked with observing the new moon have a sense of responsibility and know on which day they are expected to observe it, so they d

I would guess that the people tasked with observing the new moon have a sense of responsibility and know on which day they are expected to observe it, so they do the right thing. It's easy enough to avoid observing the new moon too early: just don't look at the sunset on the day before. Making sure you do observe the new moon on the right day is harder, but if you have several observatories you can probably manage it without self-deception almost every time.