I think you’re on the right track. My guess would be that they have a 3% tolerance (uncertainty, idk) with filling so they fill 600 ml but statistically it might be as much as 618. Putting 618 on the packaging lowers the price per liter a little, compared to 600.
618ml equates exactly to 600ml + 3% - maybe manufacturers add 3% on top because that’s the maximum allowable variance in quantities?
From a quick search, 412ml and 515ml both seem pretty common too.
I think you’re on the right track. My guess would be that they have a 3% tolerance (uncertainty, idk) with filling so they fill 600 ml but statistically it might be as much as 618. Putting 618 on the packaging lowers the price per liter a little, compared to 600.
This is pretty compelling. I vote “solved”.