The Temple Scroll gives the dates for the DSS writers.
When it comes to the Pharisees and Sadducees you have to read "between the lines" because EVERYONE uses the words "Sunday" and or after the "High Sabbath", etc.
Now those of us (Lunar Sabbath folks)who understand there was not a "High Sabbath" and then a "weekly Sabbath" a few days later, have to do some thinking as to what was originally meant.
The Pharisees wanted to wave the sheaf after the High Sabbath I believe was on Nisan 16 because Sivan 6 is very close to the date you get when counting a week of weeks and a day.
The Sadducees wanted to wave the sheaf on the "Sunday after the weekly Sabbath". The "Sunday" after the weekly Sabbath would be the first day of the week and the weekly Sabbath would be on the 22nd so.... the 23rd of Nisan would have been the the first day of the week. This would give you roughly Sivan 15/16 for Shavuot and that is when the Sadducees wanted to have the Feast (still on a "Sunday" which was more important than the date). The Sadducees did not link Shavuot with giving of the Torah.
Again, the timing of the New Grain Pentecost (Sivan 7 roughly) and New Wine Pentecost (Av 1 roughly) have the New Covenant behind them and the chronology of Exodus as well so that's what I'm going to stick with even though the dates might be different in the DSS.
An interesting sidenote I discovered is the in the year 30 CE the Essenes Passover date was the Day Before the most observed date. This is the only year in Yahusha's life that this would occure. This would explain the confusion of why some gospels mention that day as a Passover. Well, it was the Essene Passover date.
Just another curveball!
Cindy