I have had a couple packages sent from USPS around the 20th of June by different people, however none of them have arrived.

I also received a package this morning which was shipped USPS Priority International Flat Rate, which was shipped only on the 26th of June.

In my experience, there usually isn't that much difference in delivery time between Priority Flat Rate and First Class, and they both usually arrive around 7-8 days, so is there some kind of reason why First Class could be taking this long? I'm starting to get a bit worried.

I called my post office here in New Zealand, but they just tell me they can't check anything because First Class doesn't have proper tracking...