And fantasy it is. Heard back from the estate and they have never produced, nor intend to produce, such a format.
Adding in actual email: “we have never made 9-Liters of Cerretta (and our wines in general) and neither do we plan on producing these bottle sizes in the future”
I do remember seeing some old 15L (?) Monfortinos in the past.
Estate did clarify with me further, “the largest format that we product (but not every year!) is the 3-liter”. This comment may be limited to Cerretta.
The regulation for jeroboams changed about seven or eight years ago. I’ve aged and opened at least a hundred jeroboams (or larger) of Champagne and have had very, very few occasions when there was an issue.