Multiple endpoints for an audio interface?

[jb]

On http://www.usbmadesimple.co.uk/ums_4.htm it says:

   

For example a VOIP phone might have one audio class interface with 2 endpoints for transferring audio in each direction

however, the USB Audio spec (1.0/2.0/3.0) says:

   

Each AudioStreaming interface can have at most one isochronous data endpoint.

So is this incorrect?  The VoIP in and out streams would need to be separate interfaces?

https://docs.microsoft.com/en-us/windows-hardware/drivers/audio/usb-2-0-audio-drivers similarly says:

Each non-zero alternate setting must specify an isochronous data endpoint, and optionally a feedback endpoint.

[Jan Axelson]

The spec is the final word so I believe the answer is yes.