The cable net runs under the South stand does it not? It doesn't support the South stand roof at all and regardless of 1,2 or 3 tiers, the North stand roof won't be any different. They could duplicate the South stand and leave the cable net supporting the E & W roofs but it restricts the height of the S stand due to line of sight. I can see them replacing the E & W roofs at the same time as expanding the N stand so they can finally remove the entire cable net system. That may explain the delay as much as anything.