You can try a death certificate from NYC. You can get the form on-line at the New York City website, and since the hospital is in one of the five boroughs of NYC you can request a death certificate from the city. You don't have to know the exact date of death, the cost is $15 and it covers a 3 year span. In other words, you estimate 1920 and they will search 1919, 1920 and 1921. Worth a shot since you have a short window you want to try. Hope this helps if you haven't tried this already.