My point is neither more nor less than that the pattern I mentioned suggests a possible connection between the crimes mentioned. I think references to historical miscellany is a more common thing than references to numerology in patterns of killers. That said, simple numerical patterns in killings can be a way for the murderer to emphasize a connection that exists to something else. As for 2-13-17 being 7-13-12 backwards, that could well be something intentional and reflective of some other connection (that I haven't found). References to historical stuff, on the other hand, gives opportunity to reference death (which serial killers tend to like, e.g., by way of justifying killing), and it may even give a killer superficial airs of sacredness since most people who reference the dead do so more from memorialization than for perverse reasons. It is a good thing to learn how to avoid pointless death, to seek justice, and to consider what the desires of the dead would be (even those who believe in ghosts will probably admit that not being alive makes one more powerless), and serial killers may want to blend in with those who give the dead such reverence as is just. Pure numerical references, on the other hand, lead to what? Mathematics? Mathematics is not very haunting, presumably because intuitively it in itself possesses a moral neutrality that makes it not something that in itself could encourage people to kill. That forwards is like backwards is not totally a morally neutral idea, though--that is a pattern one might see for its own sake (even with words--I remember back in the day some people thought you could find all sorts of weird hellish things by playing records backwards on the turntable).
Crazy is not so bad for finding serial killers. Crazy people know that when they are extra crazy (in the typical terrifying hellish way) that they are probably on wrong track or are not going about things as well as they could, which helps them refine their understanding. It's a sense those who are never crazy may lack. In looking for "crazy" patterns, I find it helps to be in a frame of mind that is not as careful about typical common sense distinctions as usual, and so after I feel I may have found something, I find it very useful to step back away from blurry-land for a while to make sure I got everything exactly right about names, dates, etc. Often I'll notice I was off about something, which makes for gloom, then, no, I'll (often) see I wasn't as off as I thought because I'm off about something else that cancels or I am neglecting to account for something else, etc. In a way the craziest thing you can do is to be too crazy about not becoming crazy.