Dudum siquidem

Dudum_siquidem was a Papal Bull giving the Catholic monarchs Isabella of Castile and Ferdinand II of Aragon ownership of lands discovered in the New World or in India.  For my purpose, I am interested in the date on the document:

Datum Rome apud Sanctum Petrum, anno Incarnationis Dominice millesimo quadringentesimo nonagesimo tertio, sexto kalendas Octobris, pontificatus nostri anno secundo.
https://la.wikisource.org/wiki/Dudum_siquidem

I don't know any Latin but this is easily recognizable as October 6, 1493.  The English translation says 26 September 1493, so obviously the date has been retrofitted to our current calendar.

However, there is some doubt to its authenticity:
According to the American historian Frances Gardiner Davenport, no copy of this bull has been found in the records of the Vatican, but in the General Archive of the Indies in Seville two original manuscripts of it survive, both with the papal lead seal attached, although not marked "Registrata", as is usual. Until these originals of the bull were revealed during the 20th century, there was some doubt about the authenticity of what had been quoted from it. [Wikipedia]

I think there is some chance that this was a forgery.  Why would copies be found in Seville but not in Rome?  So I'm still looking for a document with an old date.