I would NOT be surprised to find new information coming to light AFTER such a well publicized sale. Where would the 'monks tale' be found before this sale - perhaps in a Spanish source. The church records? The trial of two rich monks after the discovery of a missing painting?
Why is this 'story' any different from a 'story' found in memoires? It appears that you, my friend, are predisposed to disallow any 'evidence' without clear provenance.
Where there is the thought of striking a match, there is the possibility of a fire.
Yours in firm research,
Big Al