How often does a blue Moon occur on the last day of a decade? I'd be willing to bet not very often. Organized Satanism, which always plans its activities far in advance, undoubtedly saw it coming, and decided to use it as an opportunity to send a message. It seems to me that it chose to stage a brazen example of SRA in the form of the Nisour Square massacre on the first Sunday of Ramadan, a special month for Muslims, when, according to Wikipedia's entry for Ramadan, "'Heaven's gates are opened, Hell's gates are closed, Satan is chained up and jinns are also locked up' and whoever dies will enter paradise." (I looked into "jinns" and can't fit them into my frame of reference.) So, staging a Satanic "ritual" in such a prominent location during such a holy month (when Satan is supposedly prevented from preying on people) obviously has significance, and I'll leave it up to whoever reads this decide what that is. The massacre might have been held on a Sunday because there are, or were, Christians in Iraq. As far as I can tell, the date had no inherent special significance to Satanism. The phase of the Moon was nothing special, and there don't seem to be any special numerical combinations in the date.
The plan for the massacre probably included a plan to get acquitted on the blue Moon at the end of the decade (such as by giving statements that would be forbidden to use as evidence at trial, and then using them at trial), followed on the first day of the following decade by an even more horrific atrocity disguised as "Islamic terrorism," to proclaim a theme for the entire decade of perpetual "war": impunity for Satanists to run amok, even when its criminality is obvious, but especially when it's disguised as something else (as usual). We know that Blackwater was involved in the first atrocity, and there are indications that it could have been involved in the other.