That is very reasonable and understandable to know that the sorting features were not completely launched in the state that the devs would have preferred. And thanks for informing me that it is being sorted by last change. I somewhat figured that when I added a re-watch to an anime recently and it was bumped up on my completed list.
When I say accurate, I suppose I mean that some of the anime that I have watched dating from a few months ago, to even possibly a year, are not in their correct order of when I initially watched them and they were moved to my completed list. It's almost as if when my library was transferred over from HB to the new Kitsu severs, my list got rearranged a little. Several shows have moved near the top of my list, as if I recently just watched them.
One example in my list would be Shinsekai Yori. It has moved near the top of my list, into the 9th position, and I'm fairly sure I watched that at least 5 months ago, if not more. I watched Tari Tari last month, I believe, and it is right below Shinsekai Yori. For the current way lists are being sorted, it would make sense for Shensekai Yori to be above Tari Tari if I had stated that I had re-watched it, but this isn't the case. Also, I watched Toradora in the beginning of 2015, but it is in the 13th position of my completed list, even though it was one of the earliest shows I had added in my library. Perhaps it is bumped up that much because I've re-watched it multiple times, but that was at least 6 months+ ago, so this shouldn't be the case either.
Since I haven't made any changed to these particular anime recently, especially since my library was transferred over to this new server, I do not understand why they are out of order. Anime being out of ordered from when I put them on my completed list is the only issue I'm find thus far concerning my watch list.
I hope this was a little more informative for you.