Yeah, I'd say your assumption is correct. However, other common ways that I've seen cron "fail" is for the cron entry to being installed in the wrong user's crontab, the permissions on a script changing such that it can't be executed, temporarily disabling or removing a cron job and forgetting to re-enable it, etc.

My favorite is forgetting a newline at the end of the crontab. I always put a warning at the bottom of my crontabs.

# Always end with a newline!

The most common failure I've seen is when people forget to use full paths in cron.

bash instead of /bin/bash (or similar)

There's other weirdness in cron-land too. Cron will completely ignore files containing "." .

The cron process can be killed by the oom_killer, resulting in missed crons. This may be aggrevated If the cron service is never respawned later.