Yes, I do believe that you are correct...my great grandmother lived in a small town in New Jersey, right next to a very old cemetary...when we were kids, my mom would take us through the cemetery, and we would always notice the cluster of headstones, all members in one family, and everyone died around the same time...we figured it was some sort of epidemic going around, whether flu or scarlet fever...
On the other hand, my older boy is buried in a very small cemetary, next to his favorite uncle...now his favorite uncle is buried just in front of a mass of graves of his relatives who all appear to have died in one year or the year after it, and there are about 4-5 children, and a couple of adults...I think the year on the gravestones is 1938, and 1939...one would think it was some sort of illness..
But its not...because I know what happened...the family was coming back from an evening out on New Years Eve, and they were returning home, along some country roads in Northern California...they were hit head on by a drunk driver...some of them died at the scene, so they died in 1938...a few of the others, taken to the hospital, died a few hours after midnight, and since it was New Years Eve, going into New Years Day, it was a different year altogether...
But you are certainly right about old cemetaries, one can find interesting histories, just from the clustering of gravestones...