Ned Nathan Finkelstein - Conflated people &/or missing documents

There was a Nathan Finkelstein born Sept 10, 1888, died in 1964.
He married Ruby Cora Rosenfeld. On the 1920 Census he is living in Pittsfield, MA with her, her parents and siblings, and two children.
He became a doctor.
This is a News Obit for him: https://www.newspapers.com/article/the-north-adams-transcript-obitu...
Findagrave for him is https://www.findagrave.com/memorial/64224683/nathan-finkelstein

There was a Nathan Finkelstein who also went by Ned Fink, born 1/26/90 - died 9-26-66,:
This gives his birth, death, and Military Service https://www.familysearch.org/ark:/61903/1:1:7Z34-363Z

This is the findagrave for him: https://www.findagrave.com/memorial/214273006/nathan-finkelstein

For the first Nathan, I have not yet found any records that are clearly for him after his marriage in 1912. No record for the birth of Stanley, no record confirming he died before the 1930 Census.

For the second Nathan, given the info in his obit that he "came with the family to Boston, where he was graduated from Tufts University of Medicine in 1912" - very hard to see that as the same person that was living in New York City in 1892, 1900, 1905, 1910, and 1912.

I have not yet found any records for him giving his parents nor any info on siblings he might have had.

For the third Nathan, these are pages of a Passport Application that seems to be for him:
https://www.familysearch.org/ark:/61903/3:1:3QSQ-G9X3-QDN4?view=ind...
https://www.familysearch.org/ark:/61903/3:1:3QS7-L9X3-QDDQ?view=ind...
Followed apparently by one for his wife
https://www.familysearch.org/ark:/61903/3:1:3QS7-L9X3-QD4G?view=ind...
https://www.familysearch.org/ark:/61903/3:1:3QSQ-G9X3-QDK5?view=ind...

There is a NY arrival record for that Nathan and Kate which says she was Naturalized "by marriage, March 17th 1917, New-York"
Is that Nathan and Kate G Finkelstein the same as the Nathan and Kate of the first Nathan, who got married in 1912?

I just recently found those Passport Applications and the Arrival Record.
The dates of birth on the Passport Application is Jan. 26, 1890.
Same name (Nathan Finkelstein), same DOB as the 3rd Nathan. And that Nathan apparently also went by Fink, as did the Kate who married the first Nathan.

There is at least one Tree on AncestryLibrary / Ancestry which thinks the two Kates are the same person. It currently has Nathan born 1888, no death date, with the Morris and Rebecca Finkelstein as Nathan's parents.

https://www.ancestrylibrary.com/family-tree/person/tree/68147533/pe... at AncestryLibrary

Or https://www.ancestry.com/family-tree/person/tree/68147533/person/36... at Ancestry

In case folks were wondering - in the first post - re: "On the 1925 NY Census, his wife appears as Kate Fink with ... " - how do I know that Kate Fink is the wife of that Nathan Finkelstein?
-- per Geni Kate is my second great aunt's niece, and as a result of work on that inlaw tree I was already familiar with her immediate family -- the 1912 Marriage Record gave her parents, and her residence as the same as on the 1910 Census for her and her parents - then 1925 had her living with her mother and brother and the brother's wife and child - all relatives of her I had already identified.

More progress.

Have found SSDI And California Death Index for the SAME SOCIAL SECURITY NUMBER - so for the same person - But two DOBs.
--There is SSDI for Ned Fink - b: 26 Jan 1890 -- d: Sep 1966 -- SSN Issued: NY (Before 1951) --Last Residence 92054, Oceanside, San Diego, California, USA
AND
--There is CA DI (per AncestryLibrary) for Ned Fink -- b: 26 May 1893 -- d: 26 Sep 1966 -- Death Place San Diego

There is a Gravestone for Nathan Finkelstein - with dates matching the SSDI: Jan 26 1890 and Sept 26 1966
And PFC Co K 312 Infantry - tying to VA info for "Ned Or Nathan Fink Or Finkelstein"

There is a WWII Draft Registration for
Ned Fink born May 26 1890 in Suwolk Russia - so matching the CA DI for Month and Day - with "Person who will always know your address" given as "Mrs. Rose Wiener (sister)" at the address the Rose who is sister of the first Nathan Finkelstein, and married George Wiener, is living with her husband and 2 of their children on the 1950 Census.