I searched the NGS datasheets by name and by a radial search around your coords, and did not find 47 B. I did find three others with similar names - 41 B, 42 B and 44 B, the last being the closest at 0.9 miles from your numbers. For some reason, NGS never saw fit to include this mark in the database. Why? I dunno. There are others here who may have a reasonable explanation, but my guesses would include that it was placed but never needed for the project they were working on, so never had precision elevation put on it. Did it appear stable? It may have been deemed unreliable and removed from the database. I could go on making up possibilities, but we'll probably never really know, as NGS doesn't generally explain these things.
-Matt