You say teaming was against the rules in showdown for a long while... yet this guide quite obviously says teaming is a valid way to win. No one corrected it or anything.
http://www.quickmeme.com/img/e9/e971eec69b219dc63527b63ca1c988f66a37f23beef81037f73086b6db0f8dfa.jpg (Unsupported image host)