The way I see it (and I am not an expert) is if you stop the machine and it was running on a curve it might not return to the same place. I would think you have to re start from a line number where it had been running a bit of G1 code .
I would try and experiment with some simple shapes like triangles and squares not circles.
and then try a feed hold and resume and then a stop then start ( I am not sure if pressing stop will lose steps)

If you have hit the E-stop button you would have to re home the machine ..Clive