I'm wondering how many organists really know the orchestral repertoire? Even if we play an instrument, we probably know whatever we've played in more from our own instrumental part than the score as a whole . . . Certainly that's my experience.
Accidentally I heard of a concert by the Orchestre Régional Provence Cote d'Azur in Cannes advertised on the radio so I went along to a programme of Rossini, Prokofiev and Saint-Saens. What struck me as audience rather than participant and looking as well as listening, was the extent to which composers used the woodwind section combining flute at 8ft and 4ft pitch to Clarinet or Oboe to thicken them up.
This does not always come over in recorded material where one cannot see the musicians!
Whilst translation of this is inappropriate to baroque registration, it certainly points the way in organ registration to doing likewise, even though only a singular Oboe or Clarinet might be indicated.