You can have multiple results per tracklink report. There are two types of results. An "email_open" and a "link_click". The only difference in information returned is that the "link_click" type will have an <href> element as well as the other elements.
This is the number that the PRODOCOM production system uses to identify a specific job. This will be an 8 digit alpha numeric field and is used to identify a particular job. The job_num can also be used in the PRODOCOM web portal to locate a job in the reporting option.