I have seen, perhaps you have also, that the "monk's tale" purportedly comes from the mouth of Soult himself, it would appear post Nap time, and being told on more than one occasion to visitors to his collection. Perhaps there is where we should look for 'resolution'.

I suspect that it is in contemporary Spanish sources that one must also look. I have seen reference to a particular 1800 Spanish volume, concerning Spanish paintings, that was used by Soult to locate desired paintings. I also note that buildings purported to have been 'looted' by Soult, were burned at some later date unrelated to the purported theft.