Apparently they United States Post Office has nothing to say on the subject:
You’d have better luck finding Dick Cheney’s social security number. Even though the United States Postal Service routinely hires contractors to assess performance, it doesn’t release statistics on lost mail. The post office uses something called the “External First-Class Measurement System,” or EXFC, to determine the percentage of first-class mail that travels within USPS time standards from a collection box to the addressee. Relying on those results, the post office has determined it’s doing a pretty good job. For example, the USPS reported an EXFC score of 90% nationwide last year.
The Government Accountability Office, however, has found some post office assessment criteria “unsuitable as benchmarks.” Furthermore, the post office “does not measure and report its delivery performance for most types of mail. Therefore, transparency with regard to its overall performance in timely mail delivery is limited…(so) it is difficult to hold management accountable for results and conduct independent oversight.”
So what are we suppose to think about voting-by mail’s accuracy, when they won’t even tell you or me or anyone else what percentage of mail is routinely lost by the United States Post Office?