The one detail you don't include is what my old math teacher called "the slope". How FAST it took for the book to get that low.
Looking solely at the numbers for Coates (available on your blog), we can see that after his artificially boosted debut, the comic took 20 issues to drop below 25K.
Then he had his relaunch, and the sales basically quadrupled... but in 6 issues it was lower than when his last run ended (and has stayed that way with only minor fluctuation).
I can only eyeball the numbers off of your chart, but Hudlin didn't drop below 25K until about issue #32 of his run... and sales rebounded quite a bit 5 issues later.
In general, it seems to me that Coates' run sheds readers faster than either Hudlin or Priest, which means that the gimmicks and relaunches bring the new readers in... but they don't stick around, and often take some of the base readers with them.