Thanks, Victor.
If you google for correo de mexico, or related terms, you'll find all sorts of horror stories, but perhaps some of this is outdated. I gather it has improved a little in recent years. Still horribly inefficient at best though. I bought this coin a couple of years ago (pre-covid), coming from Monclova, 150mi from the US border, and it still took 3 weeks to get to the border... Didn't help that the "registered mail" receipt was hand written and had an invalid tracking number (invalid check digit).