My first post here!
I buy all my rodents at reptile shows because its far cheaper than any I have come across in a pet store. I also don't have to pay for and mess with shipping, like I would have to if I got them online. Since I only have 2 snakes at the moment (ball python and blood python), one bag can last me quite a while. I have fed rats that have been in my freezer for 6-8 months. I guess my rule would personally be not longer than a year in the freezer, and to throw out any with freezer burn and ice crystals on the body.