Display XY Data not honoring coordinate system of input coordinate system?

[SteveRobischon]

Display XY Data not honoring coordinate system of input coordinate system - I have tabular data with lat lon columns in an unknown geographic coordinate system I need to bring into ArcMap and compare to a feature class with a known coordinate system.  I used Display XY Data three different times, each time specifying a different geographic coordinate system (NAD27, NAD83, and WGS84) for the input data.  I exported each to a new feature class and displayed them all on a map.  I expected there would be a difference in the point locations between the NAD27 and the NAD83 points, but all 3 essentially fell on top of each other.  Is there something I don't understand about the Display XY Data functionality, or is it not honoring the specification of input data coordinate systems, or what??

[MelitaKennedy]

Please post the extents, the current coordinate system, and approximately where the data should be (city, county, state, lat/lon). Once you look at the extents, you should see that they're different. One will make sense for the coordinate system and the other won't. For instance, if the coordinate system is a geographic one, the extent has to be between lat: -90 to +90 and lon: -180 to +180. If you've got coordinates larger than that, they're using a projected coordinate system. 

Melita