I just projected a feature class originally in Web Mercator (WKID 3857) to WKID 6318 (ESRI calls this "GCS_NAD_1983_2011") using ESRI's projection tool, and the same feature class to WKID 6318 (OGR calls this "NAD83(2011)") using ogr2ogr. They are very different: if I put them side by side in ArcMap they are 38" off in some places. What's more, I added the GCS_NAD_1983_2011 shapefile (the ESRI-projected shapefile) to ArcMap first and when adding the NAD83(2011) shapefile (the ogr-projected shapefile) ESRI prompted to use a transformation since they are different datums.
This is unexpected: I expected WKID 6318 to be the same between the two (ESRI and ogr). Why would they be so different?
This is the full description of GCS_NAD_1983_2011/ESRI (looking at the 'XY Coordinate System' tab in the Properties window of ArcCatalog): GCS_NAD_1983_2011 WKID: 6318 Authority: EPSG
Angular Unit: Degree (0.0174532925199433) Prime Meridian: Greenwich (0.0) Datum: D_NAD_1983_2011 Spheroid: GRS_1980 Semimajor Axis: 6378137.0 Semiminor Axis: 6356752.314140356 Inverse Flattening: 298.257222101
And this is the same info for NAD83(2011)/ogr: NAD83(2011) Authority: Custom
Angular Unit: Degree (0.0174532925199433) Prime Meridian: Greenwich (0.0) Datum: D_NAD83_National_Spatial_Reference_System_2011 Spheroid: GRS_1980 Semimajor Axis: 6378137.0 Semiminor Axis: 6356752.314140356 Inverse Flattening: 298.257222101
Everything is the same except for 'Datum'.
Why would that be? Which one is the "authoritative" datum??