MS plans are survey plans that aren't lodged at the Land Titles Office (LTO), but the cadastral information shown on them is useful to re-establish land boundaries. You can refer to and use this information if a registered surveyor certifies it as correct. You can also use an MS Plan as a basis for compilation if the Surveyor-General has examined and signed it. But it's a surveyor's responsibility to make sure that the information found in an MS Plan is reliable and correct.
Example: MS1503