Source for that "fact"?
Here's what was on the Top 300 Comic Books list for November 2015 based on info from Diamond Distributors:
1 - Dark Knight III Master Race 1 -
440,234 copies
13 - Batman 46 -
106,989 copies
17 - Batman Europa 1 -
80,721 copies
31 - Harley Quinn 22 -
58,344 copies
43 - Detective Comics 46 -
47,256 copies
45 - Batman and Robin Eternal 5 -
46,545 copies
48 - Batman and Robin Eternal 6 -
45,081 copies
51 - Batman and Robin Eternal 7 -
43,825 copies
53 - Batman and Robin Eternal 8 -
42,763 copies
64 - Batman Superman 26 -
38,056 copies
68 - Robin Son of Batman 6 -
35,633 copies
75 - Harley Quinn & Power Girl 5 -
34,127 copies
86 - Grayson 14 -
31,831 copies
94 - Batman Beyond 6 -
27,778 copies
114 - Catwoman 46 -
21,661 copies
121 - Red Hood Arsenal 6 -
19,857 copies
124 - We Are Robin 6 -
19,210 copies
125 - Batman Arkham Knight Genesis 4 -
18,843 copies
130 - Batman Arkham Knight Robin Special 1 -
17,481 copies
132 - Batman Arkham Knight 10 -
17,091 copies
151 - Batman 66 29 -
13,860 copies
161 - Midnighter 6 -
12,186 copies
171 - Bat Mite 6 -
10,961 copies
196 - Batman Endgame Directors Cut 1 -
8,884 copies
http://www.comichron.com/monthlycomi...5/2015-11.html
NOTE:
Batgirl,
Gotham Academy, and
Black Canary did not have issues released during November.
And don't forget, these numbers are primarily based on what comic book shops ordered from Diamond in the U.S., so they don't include digital sales, sales outside the U.S., etc.