Exactly what I was pointing out earlier: "Authorized" is not the same as "installed." There is no evidence that a larger tank was ever installed in a production 230SL by the factory.
Shucks, they probably "authorized" the 2.5L engine for the W113 sometime in late '65 or early '66, too, but it didn't make it into a production vehicle until the 250SL rolled out in '67 (along with the larger tank)!