No. The confusion is not that Apple fans think Apple numbers are units SOLD to end users, while Samsung or others' numbers are units merely shipped to retailers.
The fact is that you are right, "shipped = sold" ...only, it is pretty much literally correct in the case of Apple, and sold to retailer is practically assured to mean sold to end user within a couple of weeks. That's the point.
1) Apple's whole supply chain is tight and they know exactly how many and when units end up in the hands of end users. There are no containers or palettes of iPhones languishing somewhere until BOGOF deals get rid of a few more. No, no matter how big the retailer (big box, nationwide, Walmart, whatever), small numbers of iPhones are like couriered to each and every outlet
weekly. The whole chain is so tight, it's unbelievable.
That 3 million they just announced in the supply chain? That's worldwide, thousands upon thousands of sellers (big chains, big box retailers, small certified Apple resellers, Apple's own stores):
https://www.lifewire.com/where-to-buy-iphone-1999719
On that page, in US alone, I am seeing, for starters: 2200 AT&T stores, 1700 Target stores, Walmart, Sam's Club, Verizon, T-Mobile, Sprint, Staples...
Apple
has to have several million unsold in distribution network worldwide... that's like maybe 2 or 3 phones per location. But Apple is very clear about how many weeks inventory that is, they'll say 2 or 3 week's worth, and they know to a unit. And they pledge those numbers officially in earnings calls and statements; and they are more transparent in that regard than anyone else.
2) the ASP of Apple is steady (if anything, it goes up). So, that tells you something about sales. Apple could also get rid of inventory if it allowed retailers to deeply discount units or run BOGOF deals, but it doesn't. Why, because EVERY unit sells within a couple of weeks.