All,
Thank you for your responses. Patience was rewarded. It's now 5 and a half weeks since I posted my question, and the Zapotec is 7 feet tall and has at least 24 fruits in various stages.
You may be right about something removing a set fruit earlier. Just after I posted the question, there was a sudden decline in the population of small furry creatures in my garden, so maybe that's why things worked out better.
Suze, I usually have at least 3 or 4 mules every year, even years, like this one, that are otherwise generally good growing years. For example, I'm attaching a pic of Dorothy's Green taken yesterday. It was planted at the same time as the OTV Brandywine on its right and the Lillian's Yellow Heirloom on its left, treated the same, same songs sung for it, etc. I never quite get it.
As for late transplants, I have occasionally had some great results from doing so, especially from very vigorous varieties like Super Snow White or Purple Calabash. But I wouldn't try, for instance, to put in a Yellow Brandywine in July.
Best regards,
Jonathan