There is no reason that the channel spacing need limit the sideband bandwidth.
The only downside to this is that listeners on adjacent stations hear a slight "monkey chatter" from the overlapping sidebands.
This is one of many reasons why station frequencies are never allocated close to stations which are physically close.
You only need glance at the waterfall display on a good SDR receiver to see that the actual audio bandwidth is often much wider than the channel spacing implies.
The only downside to this is that listeners on adjacent stations hear a slight "monkey chatter" from the overlapping sidebands.
This is one of many reasons why station frequencies are never allocated close to stations which are physically close.
You only need glance at the waterfall display on a good SDR receiver to see that the actual audio bandwidth is often much wider than the channel spacing implies.