Many of us don't really understand this. I learned my lesson when I accidently triggered domination on the same turn as I completed the UN in COTM4. I was devastated that I had hung around the domination limit for dozens of turns to get a Diplo and then lost it at the last minute. When I check the Jason calculator to figure out what I could have scored, I was shocked to find my Dom score was the same as a Diplo score would have been (like 50 points more for Diplo).The way to medal is to milk up to the point that a victory conditions are available without having focused on them too much. Don't throw extra resources into getting to the actual victory condition ASAP, because eventually you will be able to trigger them. Even Domination usually can score better by milking things out a bit after it is possible to trigger Domination.
So the lesson here is that best dates don't really drive score. Only population and happiness drive score once you have reached the domination limit. So take a turn or two or ten and add all your workers and settlers back into your cities and get your happiness to max before you trigger your victory condition if you want your best Jason score instead of best date.
StanNP