Scottsdaledave, also curious as to why visitors were excluded from the plant for three days. Never heard your possible reason floated before, but it could be why that happened. Why I lean toward the former reason of wide bodied "mule" Z's being test run, is that folks doing Museum Delivery plant tours have reported convertibles going down the line for a few weeks, and if they were modifying some equipment or process, why would plant personnel care if visitors saw convertible assembly, or equipment modification going on (especially as Plant Manager publicly confirmed, as he did on a video about a week ago, that test assembly of convertibles is going on right now).
Again, you may be correct, and I doubt we will probably never know the real reason why visitors were excluded for three days, days when the assembly line keep on going. The good news is that public plant tours resumed today.