When you buy chicken you should freeze it within 3 days if you don't plan to cook it before or within those 3 days otherwise it can spoil.
But as long as you freeze the chicken within a few days of getting it home then the chicken is perfectly safe and good to eat well past the freeze by date.
I've kept chicken frozen for 6 to 12 and even 18 months before past the freeze by date and the chicken has always been good and safe to eat but just not as fresh as before.
If the chicken is bad it will have a foul smell and a slimy feeling to it but if it smells good and doesn't have a slimy feeling to it then it's safe to eat.
You can even keep the chicken for months and even a year or more past the use by date as long as it's kept frozen the entire time.