The fact that your copy has the B/W outstretched arm and the other copy you found that was auctioned was printed with a orange arm is curious. You would think that in an initial run, one color pallet or another would have been used for the entire run.
That's why I was offering that either yours or the orange arm version could possibly be a later reprint of the original 1915 version.
Its a matter of figuring that out. Or maybe both are first printings. It's hard to know at this point, but the fact that the orange version was ID'd as from the 1950s in that auction might be something to start with. They had to have gotten that info from somewhere, whether it's correct or not.