was it a timed job? was it untimed? check if date_conditions: 0 if so set it to 1
did someone put it on hold then change status to inactive?
that will untime as well.
the utility you want is a db lookup of jobs with date_conditions: 1 and no UP STARTJOB event.
you can also run into it where it's PD but didn't run because its on hold etc.,