Very useful information! And i suspect the amount of arguing can be vastly reduced by making a print-out of this page and taking it along:
post.gov.tw/post/internet/b_ ... 3500255027 - these are the same rules are written out in a language the average post office clerk can easily understand. Here are the relevant excerpts (with my explanation added):
(Let me know if you see any errors in the explanation...)
OK... a very important point...
Can you not apply for two PINs - a 6-digit one for domestic ATMs and a 4-digit on for abroad?