I came across the following article from the Hope of Israel website that reveals the understanding that Pentecost is 50 days after the seven complete Sabbath weeks count:

https://www.hope-of-israel.org/PhilosPentecost.html

The site itself has a number of other articles that lay out details related to this.  The article list regarding Pentecost can be found here:

https://www.hope-of-israel.org/pentecost.htm

You will need to scroll down within the smaller "List of Articles" box to find the Pentecost articles.

This next article was also a benefit to show that Shavuot (the ending of the 7 complete Sabbath weeks count only) was not the same timing as when God came down at Mt Sinai on the 17/18th day of the 3rd month:

https://www.hope-of-israel.org/sinailaw.html