In ArcMap 10.3 - Data Frame Properties - Coordinate System tab - under Current coordinate system, it will list "Authority ESRI" or "Authority EPSG" next to the coord sys definition. Examples are:
NAD 1983 (2011) California (Teale) Albers (Meters) – Authority ESRI
NAD 1983 California (Teale) Albers (Meters) – Authority EPSG
In the case of A above, that coordinate system is actually in EPSG as EPSG::6414, so is it listed as "Authority ESRI" in ArcMap 10.3 because that version of ArcMap uses an older copy of the EPSG database before EPSG::6414 was added?
Yes, that's correct. Without me double-checking, it's possible that I missed the addition to the EPSG database as well, but we now have automated scripts that compare Esri and EPSG entries and look for matches, as well as new or changed values.
EDIT, 27 April 2015: Looking at our records, we added the definition in 10.3.0, and "code changed" to match the EPSG code in 10.3.1.
