JSYK: freezer burn is just a spot of severe dehydration on the meat due to contact with air. prey items with freezer burn are 100% safe to feed *and the spots themselves will disappear after thawing.
i keep mine around 9-12 months, but some i vacuum seal with one of those food sealer-guys and they are stored for much longer. i keep f/t feeders as long as i would keep any other meats i have in the other freezer.
EDIT: *more info