Well, it's definitively not the original movement and replacing a Cal 12 with an 11 is a retrospective step - whether or not that gives you any leverage on price or not depends entirely on the seller.

It's not easy to tell from the photo, but I think I can see the "I" under the balance wheel so at least the movement should have some of the original Cal 11 problems resolved - though after this length of time, it's as much about the servicing regime previous owners have followed anyway.