Thanks Bob, that makes sense. And I am using the Gemini .Net ASCOM controller, latest version, for controlling my Losmandy G-11 mount.
What happens to the model if the plate solution is successful but perhaps incorrect e.g. say stars in the pointing image were trailed or there were clouds so that the point sources extracted from the image may not be reliable, but plate solving still returns a result which is then used for the pointing model? This has happened to me several times. Could that cause the model to deteriorate?