It doesn't help that the atomic second was defined using old data such that when it was defined we were already relatively far off from 86400 seconds/day. A re

It doesn't help that the atomic second was defined using old data such that when it was defined we were already relatively far off from 86400 seconds/day. A relatively large part of the correction being applied by leap seconds comes from this initial offset, which is also why all leap seconds so far have been in one direction. (and why the handling of the other direction is essentially completely untested, making the prospects of a negative leap second in near-ish future pretty frightening).