Madison took the notes to the convention knowing the the interpretation of the constitution, as its clauses were being proposed, debated.... finally agreed on.
Madison along with a hand full of men, on the committee of style, put the Constitution together in its current form, even making some changes.
then Madison along with 2 others, wrote the federalist which explained the document and its clauses.
Madison then throughout his life continued to write and speak about the constitution, many people wrote to Madison wanting information on it, meaning his interpretation, since he is considered the father of it.....a title he did not like.
most of the founders, did little or no work on the constitution after they left the convention, Madison though created many pieces of work, and was even sought up to his final few years to clarify the document even more...people recognized him as the utmost authority on it.