Hello,
assuming you have 20 mVpp at 1 V/div, this is 40 pp noise for 14 bits and still 10 pp noise for only 12 bits. I therefore assume that the subtle differences that can be seen with 14 bit, but not with only 12 bit, are lost in the noise. And 20 mVpp noise would be enormously good.
Best regards
egonotto