it's not uncommon for there to be mid production change units in other industries that carry parts of both years during a model change.
rather than leave parts unused they just finish using all of one thing before switching to the new whateveritis.
the car industry used to do it, or at least AMC did. my buddy's '70 AMX (per the title) had a '69 rear end, tail lights, bumper etc and it was purchased new by his dad. same thing with gibson, fender and plenty of other guitar manufacturers so i'd assume it'd be no different with weber.
leaving inventory unused is waste, and companies simply don't like waste as it cuts into the profits.
congrats on the faded beauty! very nice!