Unused and ungrounded DAC inputs are present in production models.
Unconnected and un-grounded DAC block would normally cause the model build to fail. However there is a small bug where as long as one DAC input comes from a subsystem the RCG will parse the model successfully.
This can be confusing to people who build new models that don't feed the DAC from a subsystem and the model won't build.
DAC part documentation tells users to ground unused inputs, but the RCG should either totally support DAC inputs being disconnected, or force all unused DAC inputs to be grounded.