Thanks. I'm not doubting that the signature on the front is hers... only that the attribution on the back might not be, and could be a later addition by someone else when the work was mounted/framed. I base that view partly on the handwriting, but also on the reports that she habitually signed her work 'J. Bales' because she wished not to advertise the fact that she was female (and the 'Jean' on the back gives it away).
As I said, I don't have a view on whether or not this is a print but, even as a print, it could still be an 'original' in the sense that she produced the work herself and it's not one of a longer print run nor a 'licensed-out' reproduction from an original. The purpose of a copyright mark is generally to inhibit the production of unlicensed copies.
Just as an aside, it's not unusual for artists to produce prints in two series: limited edition print runs which are either by or closely supervised by the artist, are numbered and of high quality; and unlimited print runs which are artist-authorised, may or may not be by artist-supervised, not numbered and of lesser quality. Usually, the latter are produced in sufficient volume that you'll readily find identical examples by Googling. The absence of those is a good sign for yours being an original and also, without any numbering, it's not likely to be from a limited edition print run either.
Good luck. I hope Sotheby's gives you a positive answer.
