« Reply #1 on: Tuesday 21 March 17 15:44 GMT (UK) »
Did his twin have initials AJJ Kerr? (Not putting in the full name as he may still be living).
If so it looks as though only the survivor had his birth registered with the consulate in Buenos Aires.
His consular birth certificate should reveal whether there was a year's gap between birth and registration. It isn't uncommon to find delays in these records - there was no requirement to register overseas events (and therefore no deadline) and many people would not have lived within easy reach of the British Consulate.
Ayr: Barnes, Wylie
Caithness: MacGregor
Essex: Eldred (Pebmarsh)
Gloucs: Timbrell (Winchcomb)
Hants: Stares (Wickham)
Lincs: Maw, Jackson (Epworth, Belton)
London: Pierce
Suffolk: Markham (Framlingham)
Surrey: Gosling (Richmond)
Wilts: Matthews, Tarrant (Calne, Preshute)
Worcs: Milward (Redditch)
Yorks: Beaumont, Crook, Moore, Styring (Huddersfield); Middleton (Church Fenton); Exley, Gelder (High Hoyland); Barnes, Birchinall (Sheffield); Kenyon, Wood (Cumberworth/Denby Dale)