It feels like you are implying Kay didn't work with Lennart. it's simply not true. The systemd mailling list was created in May 2010 and Kay was already registered and posting there. Check the archives. They were working on systemd from the start in a RedHat-Suse joint effort.
Also udev merge into systemd would have not happened without Kay's consent.
And I don't understand why people get downvoted just beacuse they correct you.
[Edit] Typos
I did not downvote, but my guess is because you obviously did not read the email linked to which showed the numbers with udev excluded.
udev and systemd are two separate projects who happen to live in the same repository (nothing wrong with that!) so you have to remember to exclude udev when looking at contributors for systemd.
I did read it. What does it tells you ? Well that Lennart did the commit of the first original. Has it occurred to you that they could have work together on the design ? That Kay might have reviewed/coded all or part of the prototype ?
The git can not show that. And unless Kay himself state the contrary we will not know. Lennart says Kay was associated to the project from the start. If it were not true, wouldn't have Kay said something by now ?
I don't always agree with directions Lennart goes, or on the methods. But that does not justify ferocious ad hominem attacks I've read.
I do not support the idea that Pottering wrote it without consulting people, but what is certain is that he wrote almost all of the code himself and since your comment talked about looking in git I assumed you were talking about code authorship.
Kay Sievers wrote udev, which Lennart swallowed into systemd and proceeded to make unusable outside his own pet configurations. Exclude the pre-existing udev, which was and should have remained a separate project, and it's all Lennart.