I learned from my delivery specialist that the order of VINs doesn't reflect the production schedule. Here's what he wrote:
Apparently, numerous factors play into the timing of an order's manufacturing date.
Tesla [does not produce] vehicles sequentially based on VIN. There are vehicles destined for San Diego that went into production last week with a VIN higher than yours (P635xx), and there are vehicles set to be produced the week your Model S is scheduled to, with a VIN much lower than yours (P615xx).
Apparently, numerous factors play into the timing of an order's manufacturing date.