I thought I would have found my 2nd great-grandmother, Teresa in the 1940 census fairly quickly once I had the enumeration district. The 'ED' number in the 1940 census is not the same as the 1930 census but I converted the number with the help from Steve Morse's site http://stevemorse.org/census/unified.html.
In 1930, Teresa Duper was living at 991 Flushing Avenue with two of her sons, Steven and Gerald, and her granddaughter, Eleanor (my grandmother). I found Flushing Avenue in the 1940 census and the block that my family lived on. I found building 989 but didn't see 991. I double checked the 1930 census to make sure that I had the correct address and I did. Where was 991 Flushing Avenue?
I called my mother and told her that her great-grandmother was nowhere to be found. I told her that the 1930 census had Teresa's building number as 991 but I couldn't find it in the 1940 census. My mother said that she didn't remember her great-grandmother's building having a '9' in it, she thought there was a '4'. My mother was only 7 years old when her great-grandmother did. I asked my mother if Teresa was definitely living on Flushing Avenue when she visited as a girl and the answer was "yes". My mother told me to look in the photo album with the old black/white family photos because there's a photo of Teresa leaving her building. She said that the building number is shown in the picture. found the photos while I was talking to my mother. There it is... "434". So, if this was my great-great-grandmother's address then what happened to "991"? My mother suggested that the house number might have changed but that it was on Flushing Avenue.
Later that evening, I checked the 1940 census again for address 434 Flushing Avenue. I cannot find Teresa Duper with either address on Flushing Avenue. I have to do more sleuthing.