Are you backing up your cron table?

This is, the personal cron tasks, as well as, the system cron tasks (/etc/crontab, cron.d/, cron.hourly/, cron.daily/*, etc).

Depending on the distribution you may need other files from anacron or other cron implementations, but they will be mostly configuration files for cron and no tasks.

Also note that the system crontab may reference non-standard locations. I've seen things like "/etc/cron.5minutely" debugging live servers.

At the end of the day, usually you backup everything except excludes. An unix like system, uses to have so many files, that being picking one by one needed files on backup, is not practical.

Updated (for clarity).