I was looking at all the arguments made (against the Boethians) in favor of counting the omer from 16th Nisan until Shavuot - Menachot 65/66.
Then I went looking at Leviticus 23 and Deuteronomy 16.
In Deuteronomium 16:9 it says to begin to number from the time the sickle is first put to the standing crop. But no day, time or date is given.
So Leviticus 23 needs to help to determine when we need to start to count.
It says we need to bring the omer of the first fruits of the harvest and wave it: ממחרת השבת And ביום we wave it we need to offer... and we shall eat neither bread, nor parched corn, nor fresh ears, until היום הזה. And we shall count unto us from: ממחרת השבת. That is: מיום that we brought the sheaf of the waving; its duration: שבע שבתות תמימת תהיינה.
עד ממחרת השבת השביעת we count חמשים יום.
The start and duration are clear, but how was it determined that the words ממחרת השבת had to be referring to the Pesach week? Why did ‘the time the sickle was first put to the standing crop’ needed to be a fixed time? As a farmer, we normally look at our harvest to see when the time is right to put a sickle to it. So why (please forgive me for my horrible Hebrew grammar) couldn’t it refer to the ממחרת השבת של הניף את העמר? - the morrow after the שבת, which is היום, one waves the omer. I.e. at the moment these actions take place you need to start to count. In such a case the court could determine each year when one had to harvest and when one needed to wave and start the count.