In the M9 example I have loaded a shape file in GDA94 MGA zone 50 EPSG 283500
M9 has correctly assigned this CRS from a prj file.
Initially I copied the drawing, and repaired projection to GDA2020/MGA zone 50 EPSG 7850
I put both drawings in a map and they overlaid perfectly.
Going to reproduce this I realised that the copy and paste of the drawing made a new drawing from the same table so thought that might have been my issue.
I have now tried re-importing from shape file for the comparison, however and have the same result.
I know it doesn't make sense to repair the initial projection incorrectly, however it seems like a useful way to check the conversions are working. I don't think I have any data supplied in GDA2020, but we are about to be asked to provide data in this format.
I've attached the test file. Same dataset imported 3 times.
One as imported GDA94
One 'repaired' to GDA2020
One reprojected to GDA2020
The 'repaired' one should be about 1.8m out from the others in the map, due to having the wrong CRS assigned, but it is not.