The Sanhedrin of Jesus day accounted for such times as this where the closes new moon to the spring equinox would be in such a way that the barley was not ready to harvest. Why is this important and why was this criteria required also?
Jesus said "take life's water free" while celebrating the Festival of Tabernacles. Hence precedence is set in that Jesus observed this holiday or gave it some importance. It seems reasonable then to follow the 13th adjustment month much like the Sanhedrin would have in order to keep the festivals in tact as to date.
How would you have for example the festival of firstfruits when the barley could not be harvested yet? You can check the barley report in Jerusalem yourself.
Under the current date the Watchtower has chosen for the memorial I see no way possible to correlate the rest of the festivals appropriately. Leviticus 23:39 for example discusses when the Festival of Tabernacles was to be. I don't see how this festival could have been celebrated and still follow this command from God given the date the Watchtower has chosen if Jesus were alive today.
I think the issue here lies in the fact that the Watchtower has chosen to take only one piece of criteria the Sanhedrin used back in Jesus day as opposed to all the criteria use to ensure proper celebration dates.