I am with Paul & Jay 100% on this one. I was always taught, "if you can't find the nail, don't use the course." Some measurements from landmarks are very obvious; others, not so much. We should not depend on descriptions to relocate a nail, even on our own cal courses.
I have one cal course where snowplows seem to catch my endpoint every winter, even though I use a PK nail driven flusher than flush. One year I found a clearly demarcated divot and put in a new nail, but another time could not so remeasured.
It's a great teaching opportunity for new measurers, since we don't often lay out cal courses. And since an accurate cal course is the foundation upon which all other measurement accuracy is based, it only makes sense to do it properly.