Sure, or he might have caught it and decided to run with it instead of fixing it too, but I also wasn't trying to imply that the guy who writes detective novels doesn't like to scatter mysteries in front of his readers. I'm sure there are tons of deliberate things like that, I just think not all of them are, and that also many were oopses that, because he's a good writer, he decided to change from oops into story. Why admit to or ignore a mistake when a little creativity makes it into a new mystery for the audience to enjoy?

Butters appeals to geeks, of which Butcher and much of his fanbase are. The thing is that returns to the point, Butter's has Shiro's sword, which was given to Harry to pass on in the same book Butters was a planned one-off, now common sense says Butcher probably didn't have Butters in mind to inherit, meaning either Butcher didn't know who he'd give it to or planned someone else. I'd bet on Murphy, she's obviously meant to be seen by the audience as the frontrunner and of course she did inherit between Shiro and Butters, but I think he meant it to be more permanent and changed his mind. But either way he changed it or didn't have it, and that's a fairly major plotline in the series after it was well-developed, so Lash/daughter2.0 switch isn't hard for me to consider probable.