It doesn't explain it because in LE the NTP request comes from ConnMan not "ntpd" and there is no issue with the boot date/time starting in May and then being corrected to current time; unless the configured NTP server(s) fail to respond. Unless you explicitly define servers for a ConnMan service, it will use ntp.org servers. Some ISPs and network routers block requests to ntp.org (no idea why, but it does happen) and some routers will set themselves as the time source via DHCP. If you look at the systemd journal it will show requests being made, where they were made, and what the outcome was.