I'm guessing it was in the 1990's. It must have been during a budget crunch, and, after the War Years they had way too many field divisions in Suppression. Somewhere along the way Divisions 4, 5, 9, 10, 12, 16, and 17 disappeared.
Then, someone (with too much toilet training at a young age) decided to renumber the divisions to reflect the lower number.
In the event, the Sixth Division became the Third. The symbolism in the patch explains the change- on several levels.
The irony of the merry pirates of the 6th becoming the dandies of the 3rd is beyond measure.
Luckily, after a year or two, sanity returned and the historical nomenclature resumed.
In the 1950's, the 6th Division did not exist ; only the 7th in the Bronx (on Intervale Ave.).