onecallback.js

znRecordOverlay.open({
	onSubmit: function(submittedData, onComplete) {
		var newRecord = {};
		angular.extend(newRecord, submittedData);
		console.log(newRecord.id); // error
		$scope.recordList.push(submittedData);
		onComplete.then(function(serverData) {
			// each onSave and "included" onComplete promise are connected by being in closure together
			// you can have as many as you want and they won't interact with each other
			angular.extend(newRecord, serverData);
			console.log(newRecord.id); // works
		});
	}
});

twocallbacks.js

var newRecords = {};
znRecordOverlay.open({
	onSubmit: function(recordData) {
		console.log(recordData.id); // error
		newRecords[recordData.localId] = recordData;
		$scope.recordList.push(newRecords[recordData.localId]);
	},
	onComplete: function(moreData) {
		// Need to use localId or something else to know which "onSubmit" record this ties to
		angular.extend(newRecords[moreData.localId], moreData); // need to make sure "localId" is provided here
		console.log(newRecords[moreData.localId].id); // works
	}
});

// If you're working with multiple records you can use only "onComplete" to keep it simpler
// But then you're using 2 different paradigms for single vs. multiple