Hey Brian,
I think the NOVALUE you see are just here to remind you if the selected points where adjacent or not in the original channel. I don't see any explanation in the Help though... But as the NOVALUE do not interact with vizualization or calculations that should be fine right ?
As for the Flags question :
1) "Set Flags" just selects an existing point on your curve.
2) "Set Data Point and Flag" adds a new point on your curve (e.g for future interpolation) and selects it with a flag.
At least that's my understanding.
Maxime -- Kudos are a great way to say thank you