Debian Linux - Ubuntu - Logs cleared for last and lastb, but not /var/log/auth.log after new year

So like the title says, I logged into my server and I noticed last and lastb seem to have been reset sometime before 00:48 after the new year.

Is this intentional to have it reset, or does it only display the current year's? Or should I be concerned that someone has gotten access to my server?

I do have SSH and HTTP port forwarded out of my network - so it's a live server.