Although the two new smartphone models will go on sale Sept 19 in the United States and other markets, Apple is yet to set a release date for China, the world's biggest smartphone market.
The staggered debut is a departure from one year ago, when Apple released the iPhone 5s and 5c simultaneously in 11 countries and territories including the United States, China, Hong Kong, Japan and Germany, a feat that was seen as setting a bnew standard for its supply chain and retail management.
It also comes after a 50-percent year-on-year rise in iPhone sales in China, which now carries Apple's fifth-generation phones on all of its three carriers, effectively salvaged an otherwise lacklustre second quarter for the Cupertino company.
Apple declined to comment on its latest release plans, saying only that "China is a key market for us and we will get there as soon as possible".
Chinese media speculated Apple has not yet received a routine certification from the Ministry of Industry and Information Technology (MIIT), which inspects new smartphones before they are allowed on Chinese carrier networks.
The ministry website, which notifies the public of newly approved phone models, did not list the new iPhones as of Thursday. If the MIIT certificate were the only hurdle, iPhone sales could theoretically begin as soon as they are approved.
Adding to the confusion this week was an Apple Web page that said consumers in Australia, China, Hong Kong and Singapore would be able to buy the new iPhones on Sept 26 as part of the first wave of sales in Asia.
In an overnight edit, Apple deleted the reference to the date and removed China altogether from the list of Asian markets to receive imminent iPhone shipments.
Third-party sellers and sales representatives at China Mobile's Beijing branch said the launch date had been pushed back from when they had expected, but offered differing accounts of when the phone would go on sale.
Two customer support representatives at China Mobile's Beijing subsidiary and a sales representative said Thursday they had received a staff-wide notice saying the iPhone 6 will begin shipping at the end of 2014.
A spokeswoman for China Mobile could not confirm that such a notice had been sent or otherwise provide comment. China Unicom and China Telecom could not be reached for comment.
Although Apple has never officially announced a release date in China, Chinese carriers had stoked excitement in recent weeks by taking hundreds of thousands of pre-orders for an unnamed device accompanied by a not-so-subtle number "6" graphic.
Apple's status in China has been the subject of speculation after reports emerged last month that the government has banned Apple products from official use.
Both the government and Apple have denied the reports.