Harry Stiles - New Jersey

Harry Reed Stiles was my great-grandfather. The family belief has always been that he was adopted.

I found the following info:

1870 census Blackwoodtown, New Jersey
Reed, Henry 41 NJ
Sarah 40 NJ
Stiles, Susan 34 NJ servant
Henry infant NJ

1880 census Deptford, New Jersey
Reed, Henry 52 NJ
Sarah E 51 NJ
Harry (son) 10 NJ
Barker, Irene niece 6 NJ

1900 census Mantua, New Jersey
Reed, Harry Jan 1871 NJ
Sarah E mother Aug 1829 NJ

I can't find Harry's mother, Susan anywhere else except the 1870 census. I don't know if Stiles is her married name or maiden name.

why does Harry use the last name of Reed in 1900? He used Stiles when he married.

I suspect that perhaps Susan was either Sarah or Henry's sister ..... just a hunch ..... but I haven't found any more clues and I still don't know if Susan was even married.