Quote:
Do they even use a Return to Sender post mark anymore?
I don't think "Return to Sender" rubber stamps are used much anymore, as they have given way to imprinted labels, such as this one I just received last week from a Christmas card that was sent to an old address:

For whatever it's worth, it may be interseting to note that your cover does have what I would consider a late use of a duplex cancel, though. By 1961 most of those duplex cancellation devices had been replaced by more updated ones.