The Marketing branch has been historically used in the lead up to major DLCs (the Marketing branch was not used for the Ageiversary patch with the hero cosmetic DLCs):
The first time it was used was on October 13th 2020, two days before the DE released, after that it saw no action until the first DLC.
The United States had its initial DB entry on March 17th, Marketing branch started being utilized on April 1st, and it stopped usage on April 13th, the day the DLC released.
The African Royals had its initial DB entry on March 17th, Marketing branch started being utilized on July 21st, and it mostly stopped usage on August 2nd when the DLC released, with a little blip with two depots added to it on August 9th in an update that also affected some other branches.
The Mexicans had its initial DB entry on November 9th, Marketing branch started being utilized on November 22nd, and it stopped usage on November 30th when the DLC released.
The Knights of the Mediterranean had its initial DB entry on November 9th, Marketing branch started being utilized on May 10th, and it stopped usage on May 25th when the DLC released, with a final update on June 7th to shutter it, which was the last time it was used before now.
10 mystery DLC items had their initial DB entries on May 26th, Marketing branch started being utilized on June 26th.