Smart that you found them (and cheaper than having a surveyor do it.)

The surveyors exposed our steel marker posts where they could (one was either not present or not accessible) and tied pink tape and put little flags next to them. In one case the marker is at the base of a tree, partially embedded in the roots, 6" below the surface, but they found it.

I never knew about the steel pin thing until I read a thread on here where someone described them. It's a really good thing to know!