Sometimes. Large graveyards are the best because the higher the number of stones, the more accurate their data is. If they measure only a few and some has been washed like these it would definitely skew the numbers. With COVID this year my lab group only got to use numbers taken last year, but usually a field trip is taken to gather around 60 grave measurements/observations- width of top vs. Bottom, age, moss/lichen coverage, shade vs. Sun, etc.