The newest bulletin says prior to engine # 148697. So they must have narrowed it down a bit.
"Model Type: Quattroporte Automatic (M139) & GranTurismo (M145) Model Year: 2007 to 2009 Subject: Addendum - Noise from variator Date:*8/10/2018** Bulletin*No:*MTB‐200917G* Supersedes:*MTB‐200917F* Section:**Engine** Maserati Quattroporte and GranTurismo vehicles with wet sump engine, with an engine number prior to 148697, may be affected by two different types of timing variator noise. In the event of a customer complaint of the noise from variator at cold start or when releasing the throttle in above mentioned vehicles, verify the engine number and follow the flow chart shown on following page."
For reference, my 2011 4.7 is engine # 173XXX
2011 Quattroporte S, 1987 425i biturbo