pirate, I think you are confusing production tubing with the casing. This is oversimplified but the production tubing runs down inside the casing through the packers. The production string can handle four target zones, if all are productive, using packers to separate the zones. But since they presumably left the production string in the hole after the first completion attempt, they first pull the string back out and then drop the gun down into the casing to re-perforate. Then, of course assuming it makes a well, they get the engineers like GS and jwall to design the final completion with treatment, string, packers, etc. (they will tell you that's the fun part)
(But GS and jwall can explain it far better than I when they get back on the board.)