Are you seeing the change in the CSA or the MSA? Or both?
Comparing the 2018 definition of the New York CSA
408 New York-Newark, NY-NJ-CT-PA Combined Statistical Area Allentown-Bethlehem-Easton, PA-NJ Metropolitan Statistical Area Bridgeport-Stamford-Norwalk, CT Metropolitan Statistical Area East Stroudsburg, PA Metropolitan Statistical Area Kingston, NY Metropolitan Statistical Area New Haven-Milford, CT Metropolitan Statistical Area New York-Newark-Jersey City, NY-NJ-PA Metropolitan Statistical Area Torrington, CT Micropolitan Statistical Area Trenton, NJ Metropolitan Statistical Area
https://www.whitehouse.gov/wp-conten...03-Final.pdf?#
To the 2020 definition
408 New York-Newark, NY-NJ-CT-PA Combined Statistical Area
Bridgeport-Stamford-Norwalk, CT Metropolitan Statistical Area
East Stroudsburg, PA Metropolitan Statistical Area
Kingston, NY Metropolitan Statistical Area
New Haven-Milford, CT Metropolitan Statistical Area
New York-Newark-Jersey City, NY-NJ-PA Metropolitan Statistical Area
Poughkeepsie-Newburgh-Middletown, NY Metropolitan Statistical Area
Torrington, CT Micropolitan Statistical Area
Trenton-Princeton, NJ Metropolitan Statistical Area
https://www.whitehouse.gov/wp-conten...in-20-01.pdf?#
It looks like NY lost
Allentown-Bethlehem-Easton, PA-NJ Metropolitan Statistical Area
and gained
Poughkeepsie-Newburgh-Middletown, NY Metropolitan Statistical Area
The former was 844k and the later is 679k, so that's might be a significant chunk of the difference.
Edit: Actually, looks like the later was just restoring a MSA, so that's probably most of the difference. For both CSA changes and MSA changes
"In February 2013, the MSA was deleted, and the constituent counties became part of the New York-Newark-Jersey City, NY-NJ-PA Metropolitan Statistical Areas.[4] During this time, the counties were split into two metropolitan divisions: Orange County was a part of the New York-Jersey City-White Plains, NY-NJ Metropolitan Division, while Dutchess County was in the Dutchess County-Putnam County, NY Metropolitan Division.[5]. The MSA was restored as a separate entity in September 2018.[6]"
https://en.wikipedia.org/wiki/Poughk...ropolitan_area