An offer wouldn't need to be disclosed; a deal would. That is, an accepted offer. But a straight-up offer would be non-standard. Rather, there would be an NDA/CA entered into, then a non-binding term sheet would be negotiated setting forth the material terms/outline of the deal. After the term sheet is agreed to, they would proceed to negotiating definitive agreements. While a company might disclose the execution of a term sheet, it wouldn't have to. Rather, just the definitive agreement would need to be disclosed.