All knots are bleached. Some suppliers bleach only the front but Toplace bleaches all the knots. It’s a default setting for all orders and there’s no extra charge for it. And you’re right about #1b and the darker colors being tougher to bleach. The darker the color the longer bleaching time required. Bleach too long and it harms the strength of the hair. Bleach too little and some of the knot is visible. Some people with dark hair specifiy that only the front 1” be done in blonde hair (#22) and then they color it darker--just depends on how critical you are on your hair.
John