I've been to the cemetery at Longtower too and the newspaper story explains why there are very few graves!
My family were not only lifelong members of Longtower but, they also donated large sums of money to this church and have a memorial plaque on the wall inside.
(I've been told that part of a large donation made in 1929 paid for the existing baptismal font)
I have since located most of their graves in Derry and not one of them is buried at Longtower !
Deaths range from 1867 to 1945
Early deaths were buried at Killea burial ground whilst those from 1884 onwards were buried at City Cemetery, Lonemoor