So, this weekend I saw that a group was celebrating Shavuot this past Sunday which is nearly a month later than what we have celebrated it. It made me wonder how people in this community take their "signal" as to the 1st of Abib/Aviv.
My house has since 2016 looked at https://www.abibofgod.com/feastdates for our indication as they have eyewitnesses in Israel and Jerusalem. They have a whole document on https://21731d94-49a9-4f33-bba7-2f735c51036a.filesusr.com/ugd/1568d5_137fdd5dc77c41219f334abec4255f58.pdf that explains their process, and it is rather insightful.