Complex sentence: This meant that in the event that interstate clubs were to host both semi-finals or both preliminary finals, one of these matches would be moved to the MCG; this happened in the 1999 Semi-Finals and the 2004 Preliminary Finals.
Split into simpler sentences: This meant that in the event that interstate clubs were to host either both semi-finals or both preliminary finals, one of those matches would be moved to the MCG. This happened in the 1999 Semi-Finals and the 2004 Preliminary Finals.