Prewar and immediate postwar boxes had labels that were rightside up when the box was closed (see first picture below). But so far as I know all the two piece blue boxes (postwar) had them upside down (second photo). At least that's the way it is in my collection.
The story I heard many years ago was that it facilitated display. When the gun was displayed in the box, the top would be slipped under the bottom with the gun still inside. With the label mounted the way it was, the information would be readable from outside the display case, with the gun clearly visible, nestled inside its box. I remember as a kid seeing Smiths displayed this way. Nowadays, no one displays guns in the box, but back then nearly everyone did. At least in the part of the country I grew up in.