Are you not thinking about the 9-bit scheme where a ninth bit is used to tell if the byte is an address or if it is data?

This is used to allow a listener to ignore all incomming data until woken by an address match. If the ninth bit is set, it's an address byte, so the low 8 bits are matched. If the ninth bit is cleard, the listeners will either receive or ignore the data depending on if they have made an address match or not.