This particular type of button has been cussed and discussed on TNET a few times over. I think the most recent in depth discussion on whether or not this button, and especially the NA 114 from Albert's book, is actual US Navy Issue (during the CW/after the CW/way after the CW) vs it being a simple civilian button "fashioned" in the manner of the military button and made later, was last discussed on this thread
http://www.treasurenet.com/forums/what/335588-military-buttons-id-age.html
Just looking it over and then looking at your button, it does give me a moment of pause considering the age you say the area is and the fact you say you have found unquestionable CW buttons (like the Staff button you mentioned above), but I think considering the earlier 2013 thread I think this button just might be am more modern 20th century version of an older navy design. The "self shank" does appear to be pushed in a bit on yours, while many others simply rusted out as they were made of cheaper material than that being used during the war.
Could be wrong of course but the better authorities on this like TheCannonballguy and BigCypressHunter might chime in here...
For further research on this, check Ridgeway's Civil War Relic Man button site. I included a link specific to many similar CW era buttons and the corresponding Albert's or Tice's button ID.
http://relicman.com/buttons/zArchiveButtonFederalNavyC2part.htm