[clucas]

I worked as a CAD operator, surveyor, and occasional field crew worker at a civil engineering firm for a few years. We never ran into issues like this - by far the more common issue was the difference between NAVD and NGVD. At the time I was surveying, the FEMA flood insurance maps in our area were only partially updated, so the base flood elevation could be in either datum, and you had to really watch it so you didn't end up about 0.7' off vertically.