Mick Maloney's history of the banjo in the O'Conner/McNevin book/tape - 50 Solo's for Irish Tenor Banjo (or something like that) notes that various tunings, mostly in 5ths, were used and points to Barney McKenna tuning GDAE in the 60s as the start in terms of an "Irish standard tuning" emerging.
The tape has the players using differnt tunings, David McNevin plaing GDAE and all Gerry O'Connor's tunes are in CGDA.