You can eat chicken 5 days after the sell by date as long as the chicken has been kept frozen and has not actually spoiled.
Chicken can remain safe well past it's sell by date and even for several years as long as it's kept frozen during that time.
The freezing temperatures helps prevent bacteria from growing on the chicken and other meats which makes them safe for many years frozen.
I've eaten chicken that I've had frozen for 5 years and it was still very safe to eat although the taste changed a bit.
When the raw chicken is kept in the refrigerator it will last for around 3 days but when in the freezer and kept frozen the raw chicken lasts longer.
Cooked chicken in the refrigerator can last 5 to 7 days but it's best to eat it before that.
When raw chicken is bad it will have a bad smell to it, have a slimy texture and can even change colors.
If the chicken smells good and is not slimy and has been kept frozen you can safely eat the chicken 5 days or longer past the sell by date.
But if it has signs of spoilage it should be thrown out.