Your first one is a point in the rectangular grid of the Public Land Survey System and was placed by licensed surveyor #3550. The second one looks to be a brand new (dated 2013) point set by the COE and may or may not make it into the NGS database at some point in the future; but for sure will never be part of the GEOCACHE game. MEL
Thank you for your timely response. Markers are within a few meters of each other and the second was set in June, I believe, near a railroad spur feeding a soon-to-be-defunct power plant. Since I could not locate them in any database, I was unsure what part (if any) they would play in Geocaching. You've been extremely helpful .. thank you!