Snow Tires and slippage

We usually go all winter with all season tires but this year we got proper snow tires. I didn't think we'd got our money's worth out of them so luckily we've been dumped on by a fresh few inches and be sliding around for at least one last day. Today I scanned all of the negatives I shot with the stereoscopic camera over bast week (4 rolls). I have a slippage problem on some rolls which creates superimpositions. I think it happens commonly about half way through the roll but I'm not sure what to do about it now. Do I just stop at the half way point (wasting half the roll but paying full processing)? Probably.