Keeping in mind that the "D.S." came out in the late 20's as a 2" P.P.S.,anything is possible. But the 50's sounds a little late. Unless,of course,Colt employees "found" some earlier labels/boxes at that late date while doing an "inventory"/parts clean up.
Some of us have learned "never to say never(made or used)",when it comes to guns/accessories,that don't seem to fit the dating that some "experts"(?) seem to have etched in stone.
Of course the serial number of the D.S.(or P.P.S.) will play a major role in determining "originality.
They were marked as both PP & DS. I let my boxed DS go a couple of months ago. A PP box was used and an additional label was attached that read "Detective Special". I'll post a photo of the end label on my Bankers for illustration.