In 2002, Polyhedron became a sub-section of Dungeon magazine. It continued to run until August2004, when Dungeon editor Erik Mona discontinued Polyhedron and refocused the magazine purely on Dungeons and Dragons content.
Issues from the single issues of Polyhedron are considered 'non-cannon' however may contain ambigously-canon elements. Issues printed after the merger with Dungeon are considered canon.
"I do want to clarify that the old Polyhedrons, to my knowledge are unofficial. There were a few Star Wars articles in Dungeon/Polyedron magazine that were published after April 2003 that are official."