When I went to Gilead around 1960 it was reported that one year the Society announced a wrong date for the memorial. The way the Jews calculated the passover was counting Nisan 1 from the date of the first new moon closest to the spring equinox, that can be before and after. Counting 14 days from Nisan 1, brings us the date of the passover/memorial.
Some smart ass, calculated the date and found the Society had made a mistake when the Society announced it. What did they do when the error was pointed out to them? Change it to the correct date? and acknowledge their error to the flock. No, they just wrote back to the brother, thanked him and told him to let it be. So one memorial at least was celebrated on the wrong date.
Another point of interest. Sometimes the date of the memorial differs from the Jewish passover. How come?
belbab