what does "Media Date/Time" column mean?

NBU 7.6.0.4

in NBU/Reports/Tape Reports/Images On Tape, there is a column labelled "Media Date/Time". what exactly does that mean? is it the creation date of the media or the jobs?

i have policies that have a retention of infinity and i'm trying to collect all the media it uses every month. i can sort the "Retention Period" column but to find, within that retention period, my monthly backup should i rely on the "Media Date/Time" column?

if only i could tell NBU to use a particular media ID or group of media IDs then this monthly backups will be a lot easier to handle.