Barbara,
What is missing is the lower case "o". It is easy to see where it has fallen off on the full res photo. and matches with other grave reference lettering elsewhere. If it was just an upper case "N", it would refer to Plot N, which is a long way away. As I said, looking at all the graves in those two rows along the path, the numbers duplicate. I didn't map them all out, but probably from about 700 to 715. The directions you gave me, were to a separate section of Plot A, this is not the case. The Howard grave is directly in front of the Hill grave and from these and the others adjacent, it would appear that they were originally envisaged as enlarged plots, but subsequently it was decided to make them into two graves. There is no walkway between them - the foot of one touches the head of the other. If you have access to Deceased Online, try Florence Ivy Lainson and Maggie May Larking (A.714).
Phil