One thing that can help with this is the new object type readout in the last beta.

If you've got a fully closed curve, it will say "Closed Crv" there - this one just says "Curve", which means open curve.

In the future I would like to have an area to put out various warning or error messages so that commands could give more feedback about what has happened. I haven't quite figured out where to put something like that in the UI yet though.

- Michael