The evidence (such as we have) has until now been assumed to support the view that Mozart is the true composer of 'Le Nozze di Figaro'. That view, now over 200 years old, can rightly be described as the 'traditional' one. And it's one you happen to agree with. To the best of my knowledge it has not been suggested that Mozart did NOT write this opera - until now, that is.
There are things about tradition, Frank, which only become apparent when the matter itself is suggested as being due to a different (not previously proposed) origin. In this particular case lack of evidence for Mozart/da Ponte having been commissioned, censors approving etc. etc. - such things, previously thought to be of little or no consequence suddenly become something of an issue - since these anomalies in the history of 'Figaro's' premiere are just what we might expect if the piece is NOT by Mozart/da Ponte. The very act of questioning tradition can makes us (I suggest) look anew at these previously 'unimportant' matters. And the theory of an alternative composer gains strength if it can be shown that the alternative focuses accurately on contexts within which this matter ('Figaro') first came about.
I honestly cannot help more in this request of yours for method.
Best regards
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