What flight heritage do the parts being considered have in your specific mission type (e.g., earth imaging, communication, weather monitoring) and duration?
If the parts have survived the space environment in a previous mission, this
provides useful information that could build confidence in the parts for your own application. Remember that there may be specifics of your mission type that are more (or less) stressing that could require additional or different testing or analysis to assess performance and reliability. Also, compare the respective length of the missions, which may impact reliability requirements.