A2dp optionally allows multiple codecs. Anyone can make their own. Codecs are negotiated at connection time and if the headphones and device both support a give

A2dp optionally allows multiple codecs. Anyone can make their own. Codecs are negotiated at connection time and if the headphones and device both support a given codec, they can choose to use it. SBC is mandatory, all others optional, including ones you can invent later (even after the spec is final and in use).