Some St Johns regard it as part of their surname, so for them I would have author-sort as 'St John Smyth, Ebenezer'. But the 'St' should never be separated from the 'John', as happens with Madeleine St John (Booker prize winner) - where author-sort ends up as 'John, Madeleine St', which looks like John, who lives on Madeleine Street.
If the St John pronounces it as 'sinjin' or 'sinjun' there may not a '.' after 'St'. The name was borrowed from Hebrew word meaning "God is gracious", but it got christianised into St John (the Baptist ??). IMO people who put a '.' after the 'St' should stop doing it
Why do we say words get 'borrowed' - far as I know they're never returned. Should be 'stolen' or 'pilfered'
BR