Fair disclosure is the test for whether something raised in the disclosure letter or data room actually protects you against a warranty claim. Disclosing a fact badly is, for these purposes, close to not disclosing it at all.
Technically, it is the standard requiring a disclosed matter to be revealed with enough detail for a reasonable buyer to understand its nature, scope, and consequences, not merely referenced or alluded to. A document sitting in a data room folder does not automatically constitute fair disclosure of everything it contains.
The buyer wants a demanding fair disclosure standard, so only clearly flagged, specifically explained matters qualify the warranties. The seller, at the drafting stage, wants a more forgiving standard that gives broader effect to whatever was made available, however it was presented.
In practice this is less about the drafting and more about the seller’s own discipline. However the standard is defined, a one-line reference buried in a long index will rarely survive a dispute, while a clear paragraph in the disclosure letter explaining what the issue is and why it matters usually will.
What you as a seller should push back on: a fair disclosure standard drafted so strictly that only word-for-word itemised disclosures qualify. And disclose the matters that concern you specifically and in plain language, rather than relying on data room volume to carry the protection.