I have chickens in the freezing box. How long can I keep my fatty chicken legs there until they become dangerous to eat? How should I defreeze the chicken? Can I just put it to the hot water or should I slowly warm it up to boiling water? How does freezing chicken cooking differ with non-freezing chicken?
I make stock from my leftover chicken bones and vegetable scraps. I just dump them in the pot still frozen, cover with cold water, and heat until it's a bare simmer. Simmer the stock for 2-3 hours or so, or until it tastes like soup instead of water. (But be careful not to boil, since the stock can get cloudy if you let it get up to a full 100C.) I have made this with both cooked meat and uncooked.
Uncooked chicken (whether frozen or not) will give you a mildly-flavored white chicken stock. If you brown the meat first, you'll get a stronger flavor and a brown chicken stock. (See here for a discussion.) If your chicken isn't cooked, you'll want to roast it to get all the nice brown bits from the Maillard reaction, which will defrost the chicken in the process.
I can't say anything about the first question, but a few months in the freezer won't make it a dangerous eat, IMO.
You should defreeze the chicken, preferably, overnight in the fridge in the plastic wrap you used in the freezer.
If you don't have time, just dump it in cold water and bring to a boil. Some say over a high heat, others over a low heat. I say, high heat goes faster so it should be watched more closely. You have to prevent the rolling boil and go for the simmer. And scope the foam of the water (around 70ºC).
Do not put the chicken in hot water.
I have no idea how a frozen defrozen chicken differs from an unfrozen chicken.