You really think Tim Cook says truth? He will say anything to get the pofit moving. Just looking at his China business model, tells you how truthful he is.
Do you really think that Cook would lie during a Investor Conference Call?
There must be dozens (even dozens of dozens) of people at Apple that know the exact model sales breakdown. If Tim Cook says that the X is the best selling model every week since it's been available, then that's the truth.
Now, if he doesn't specifically say it at this quarter's call, then you'll know something is up. Even if he says it differently, you'll be able to read into what he's saying.
Examples.
1. iPhone X was the best selling model this quarter. - this would signal that another iPhone model had better sales for at least one week of the quarter, but the X sold more overall. to me, this would not be a big deal.
2. iPhone X was the best selling model every week in the Asia market - this would signal that the X was outsold in most other markets and probably worldwide. this would be bad.
3. doesn't say anything - this would signal that X did not sell well anywhere when compared to other models, specifically the 8plus (the CIRP survey data is indicating that the plus outsold the X by a wide margin in the US). This would be really bad.
Most of these statements will be sliced and diced by the analysts to try to figure out the breakdown. The ASP will provide a sanity check. If the analysis is bad X sales and the ASP drops, look for AAPL to tumble badly.
If the X remains the best seller and the ASP is steady (and the overall units sold is decent), look for AAPL to remain steady.