On your Solaris boxes here, you’d need to do
last -10 reboot to actually get the times that the system was rebooted.
As it shows the system down messages, as well as the boot messages.
root@immam # last -10 reboot reboot system boot Sun Aug 16 10:53 reboot system down Sun Jun 14 08:50 reboot system boot Sun Jun 14 08:17 reboot system down Mon Mar 2 12:44 reboot system boot Mon Jan 27 10:23 reboot system down Sun Jan 26 13:15 reboot system boot Sun Jan 26 12:36 reboot system down Wed Jan 22 14:40 reboot system boot Mon Jan 20 13:55 reboot system down Mon Jan 20 12:59