you need to make sure you are in the right coordinate system, artboard or global. if you are in global, your first artboard probably started at 0,0. after you moved it the new coordinate for your path should be width / 2 + 0.5 * 8.5 + the artboards left position. same for the y coordinate.
Can you please suggest how to switch to the global coordinate system?
to convert coordinate systems use
the parameters 'source' and 'destinations' are the systems and there are called
i don't think you need to do any switching between the 2, you need to get the artboard rectangle and add it's position to the position you want for your guides. so if artboard 2 is at 25,50. you need to add 25 and 50 accordingly to your path's coordinates