This case is going to cause some problems.
Normally, if Client A and Lawyer A have a confidential communication, disclosure of it to a third party waives any privilege. However, if Client A and the third party have a “common interest,” there is no waiver. So, for example, if a licensor communicates with patent prosecution counsel for the licensee about prosecution of a foreign counterpart of the licensed patent, there might be a privilege.
But not under New York law. The Court of Appeals, inaptly named highest court of New York, held that only if there is pending or anticipated litigation is the common interest exception to waiver available. Ambac Assurance Corp. v. Countrywide Home Loans, Inc., (June 9, 2016).