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I am unsure where you are in the world but in the UK we have star ratings on our freezers.
So raw chicken in a 3 *** rated freezer will be good for at least 4Months. This is -18c or 0F, 1 star is -6c, and 2 stars is -12c.
Cooked chicken kept at -18c will last indefinitely!
If I were you I would throw it out immediately. A science channel taught me that chicken contains really harmful bacteria that could severely damage you or threaten your life, so throwing it out is a life saving choice.
Chef here, you have nothing to worry about. While foods frozen past 2 months are at risk of being freezer-burned and thus having their taste and texture affected, as long as you cook the chicken thoroughly as you normally would, there are no health concerns. If you notice ice crystals are covering the chicken breasts this is freezer burn; again, it’s not dangerous.
I usually go to this site when I have a question. I just pop the item in the search bar and scroll past the first 3or 4 ad results to get to the relevant page. Here’s the page for chicken.
http://www.eatbydate.com/proteins/poultry/how-long-does-chicken-last-shelf-life-expiration-date/
The chart says fresh chicken unopened lasts in the freezer for 1 year past the printed date.