When a kernel commit starts with "In A.D. 1582 Pope Gregory XIII found that ..." you know you're in for a ride:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f076ef44a44d02ed91543f820c14c2c7dff53716
tl;dr: Rockchip decided November should have 31 days...
rtc: rk808: Compensate for Rockchip calendar deviation on November 31st - kernel/git/torvalds/linux.git - Linux kernel source tree

@kees It's so unfathomably ridiculous how hardware vendors think it makes any sense to store and compute broken-down time rather than POSIX or TAI.