With more than enough demand for Apple's (NASDAQ:AAPL) newest iPhones during the company's fiscal first quarter, iPhone sales during the three months will be mostly dependent on how many iPhones it could produce -- a storyline that has played out again and again every iPhone launch since 2007. This means following indicators of Apple's iPhone supply progress during the crucial quarter provides some insight into how well the tech giant may perform. Fortunately, Apple seems to have wrapped up its holiday quarter with supply nearly in line with demand.

iPhone 6. Image source: Apple.

Big iPhone 6 demand is making robust supply difficult
It was clear after Apple's iPhone 6 launch weekend that the tech giant hit a home run with its 4.7-inch iPhone 6 and its 5.5-inch iPhone 6 Plus. Even without China included in the initial launch countries for the new iPhone lineup, as it was for the iPhone 5s and 5c, Apple set a new launch weekend sales record of 10 million iPhones, up from 9 million for the iPhone launch in 2013. But, as usual, launch sales during the weekend were limited by supply. Many versions of the iPhone quickly sold out both in stores and online.

Catching supply up to demand this year, however, is proving to be more of a challenge than it was last year. Retail store availability of the new iPhone models and online shipping times have, so far, lagged behind respective availability and shipping times for the 5s and 5c last year. This trend continues into 2015, though the difference from the year-ago period of iPhone supply indicators with those today is closing.

In early December, the 16 and 64 GB versions of the iPhone 6 and iPhone 6 Plus were showing shipping times of three to five business days in the U.S. online Apple Store, while the 128 GB versions of the iPhone 6 and iPhone 6 Plus had a shipping time of seven to 10 business days. At that same point one year ago, the 5c was available to ship within 24 hours and all versions of the iPhone 5s were shipping within one to three business days.

Today, most versions of the iPhone 6 and 6 Plus are shipping within one business day, while a few are shipping within three to five business days. This time last year, all new iPhone models had a shipping time of "within 24 hours." 

iPhone 5s in Apple retail store.

A similar storyline of better availability for Apple's 5s and 5c last year compared to the 6 and 6 Plus this year has been playing out in Apple's retail stores. Even in a the second half of December, 22% of 80 Apple retail stores Piper Jaffray checked with didn't have all iPhone 6 models in stock. At the same time last year, however, virtually every Apple retail store appeared to have all models of the 5c and 5s in stock.

Based on a number of surveys and estimates, and Apple's historical ability to easily boost year-over-year iPhone supply during Q1, it's very likely that Apple's slower progress in catching up with demand for the iPhone this year versus last year is related to a big year-over-year jump in demand -- not supply problems. This is why analysts, on average, are expecting Apple to report record results in Q1, with revenue up 15% from the year-ago quarter. And with Apple ending 2014 with indications that iPhone supply is very close to demand, it's looking like analysts expectations for record iPhone sales in Q1 will turn out to be true.