Day-books, diaries and files found on company premises can support an adjustment of revenue: a generic objection is no defence.
Off-the-books documentation found at the company amounts to a serious, precise and consistent presumption: denying its relevance in general terms is not a defence.
According to the settled case law of the Italian Court of Cassation, notes, diaries and informal records containing data that never passed through the official books justify the accertamento analitico-induttivo (analytical-inductive assessment) of revenue under Article 39 of Presidential Decree 600/1973. It is for the taxpayer to provide specific evidence to the contrary, document by document.
The point also matters organisationally: internal management notes must be kept separate from tax data and stored methodically, because during an audit every entry can be read as undeclared revenue. The network assists businesses in setting up their document flows correctly and in presenting their defence in the contraddittorio (the pre-assessment exchange with the tax authorities).