Prophecy may be true or false in terms of source or content.
True prophecy is the proclamation of information as God's own words through the Holy Spirit: "Thus saith the Lord"
True prophecy may be characterized as special revelation or Scripturally aligned proclamation.
All Scripture is the result of true prophecy validated and collected by the Holy Spirit working through Man.
Not every instance of true prophecy is Scripture.
All special revelation prophesies resulting in Scripture have ceased.