The first two guns are in the AC no date serial number range but have the date code of 40 added. I presume these were still in the factory for some reason when the order came in to add the date. The last photo is courtesy of Orv Reichert and is an extremely rare 480 series with the 40 added.

Here is another example of this unusual variation. However, this gun is a bit more beat up than the other one.

Here is a photo of a 480 coded pistol with the 40 added in the collection of Orv Reichert, note that this gun also has the X mark, however it is on the slide above the serial number.