not_kevin
Veteran
WCA Regulations said:10d) All pieces of a puzzle must be fully attached to the puzzle, and in their required positions. Exceptions: see Article 5 Puzzle defects.
5b5) If, after the solve, non functional parts of the puzzle are still defect (like a centre cap of a cube) or not fully rotated (like a 5x5x5 centre piece twisted in its spot), but the puzzle is otherwise unambiguously solved, the puzzle is considered solved. (discretion of the main judge)
5b) If a puzzle defect occurs, the competitor may choose to repair the puzzle and continue the solve or choose to stop the solve.
So 10d says that the puzzle must be completely together, except for some Article 5 things. 5b5 would be the center cap, as long as the puzzle is still unambiguously solved. Now, if you have 4 centers come off, but they're not all in the same slice (so the remaining two caps are opposite), then that's ambiguous, because you can't tell where the caps would go. But if you have 4 caps fall off where the remaining two are adjacent, from that, you can unambiguously determine the color scheme.
The other thing to note is that in 5b, you have two choices. 1) Repaid and continue or 2) Stop. There is no option to keep going and repair later. I had someone try this one time, and I was going to DNF them at the end, but they DNF's anyway, so I just warned them.
Actually, you can rebuild during the solve:
WCA Regulations said:5b3) If after repairing the puzzle, but still during the solve, the competitor notices that the puzzle is unsolvable, he may disassemble and assemble max. 4 pieces to make the puzzle solvable again.