I believe that on the Lefevers guns built prior to the 1890 patent, Two-Hook style the 10 was about as common as the 12. This was also about the time smokeless powder was becoming acceptable. As time went forward, fewer & fewer 10s were built in proportion to the 12s, thus the differences in percentage.

This same timeline is likely applicable to other makes which were building doubles prior to the 1890s as well.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra