I'll bet that the Decker's did either know the mom, or more likely, almost certainly knew her identity, because as you probably know, the birth location in Hudson N.Y. State was a reformatory for girls aged up to 16, and in 1940 Stanley Decker, living at 123 Academy Avenue in Warwick in Orange County New York, was a N. ?. Reformatory Captain. !
Too far to travel to Hudson daily, but he probably had connections and contacts through work.
The letter after N is illegible, they also have a 6 month old infant called Patrick Paul, who curiously, is listed as a boarder. !
New York had a State census in 1925, and it's surprising, but in both the 1925 New York State census and in the 1940 U.S. census, there aren't very many females called Katherine or Catherine McMillan, living in new York State, and in both censuses there is only one person, the same person in both censuses, who is the correct age to be about 15 or 16 in 1941.
Catherine McMillan aged 14 in 1940, so born circa 1925 in New York.
1940 address 7214 3rd Avenue, Kings County New York City.
That's in the Bay Ridge area at the south western end of Brooklyn.
Father George McMillan 39 born New Jersey, works for N.Y. State as a printer mechanic.
Mother Catherine McMillan 40 she and the children were all born in New York.
George McMillan 17
Catherine McMillan 14
Rosella M McMillan 8
William E McMillan 2
http://en.wikipedia.org/wiki/Bay_Ridge,_Brooklynhttps://maps.google.co.uk/maps?q=7214+3rd+Ave,+Brooklyn,+NY+...http://en.wikipedia.org/wiki/New_York_Training_School_for_Gi...I wonder if the great Ella could sing like this when she was in the reformatory. ?
http://tinyurl.com/o52nuzg