Apple’s iPhone X accounted for 20% of all U.S. iPhone sales during the fourth quarter, Consumer Intelligence Research Partners said (PDF) on Monday. That was enough for the iPhone X to top the iPhone 8 Plus, which accounted for 17% of total iPhone sales during the period, but well behind the iPhone 8, which tallied 20% of sales.
Overall, the three newest iPhone models made up 61% of total iPhone sales. That was down significantly from the 72% share the iPhone 7 and iPhone 7 Plus accounted for in 2016 when they hit store shelves.
At first blush, then, the iPhone X might not seem like a breakout hit. The iPhone 7 Plus in 2016, for instance, earned more than 30% iPhone market share in its first quarter on store shelves. But CIRP partner Josh Lowitz said the iPhone X is altogether different than earlier releases.
Get Data Sheet, Fortune’s technology newsletter
“Comparisons to earlier launches are tricky at best,” Lowitz said in a statement. “First, iPhone X wasn’t available for the full quarter. The Apple model pie is further divided, as they now offer eight models, the most ever. And, Apple launched the new phones on a different schedule, announcing three new models at once, but delaying the launch of the most advanced and expensive one, iPhone X, for five weeks following the launch of iPhone 8 and 8 Plus.”
While Apple announced the iPhone X alongside the iPhone 8 and iPhone 8 Plus in September, the $1,000 handset didn’t actually reach store shelves until November. That gave the iPhone 8 and iPhone 8 Plus nearly two months of time on store shelves before the iPhone X was released. Apple kept a similar September release schedule with other previous iPhones. The fact that the iPhone X was able to reach 20% share in just a couple of months, therefore, suggests it was a reasonable success.
For its part, Apple hasn’t commented on iPhone X sales and how they compare to iPhone 8 or iPhone 8 Plus sales. But the company will hold an earnings call next month that could shed some light on exactly how well its iPhone is performing.