Ooookay, you seeing 2666 makes sense now.
Ram has changed.
It used to be that if you bought 3200 mhz ram it defaulted to 3200mhz, that's no longer true today, it defaults to the cpu speed (?), in this case 2666. You actually have to go into Bios (efi) and enable XMP (I forget the AMD name for it) and it will jump to the higher speed. I don't know why they did this, seems counter intuitive, but they did. Anyone who has an Intel, be warned, Intel is being real sh*theads about this and if you call about a CPU warranty one of the first things they ask is if you enabled XMP and if so telling you they will not cover it.
Yes, companies will swap parts if they run out but it needs to match or better the claimed part. When you said it was 2666 I was thinking that was the ram speed, not what it was running at which would indicate it had been changed. One part being changed by the factory, okay, two parts and I start seeing major red flags that someone had messed with it. You wouldn't see Dell or Apple sending out a system with a bunch of alternate parts, one maybe, two no way.
Seems like you're fine, just a misunderstanding, sorry for making you panic.
I do think you over payed on ram though.
By the way, so long as it had Win10, they couldn't really say anything when returned, you could have just uninstalled the pre-installed software, done a system refresh or if it went from home to pro you could have bought an upgrade, they wouldn't know. Regardless, first thing they would do when it came back would be to wipe it and reload the original copy of Windows it had to begin with in order to run diagnostics with known variables while at the same time removing your data. This is why when you send a system in for factory repair it often comes back wiped, it happens less these days, but it still happens.
Parts can be OEM without being white label, I've seen them slap high end stickers on garbage just to make it look higher end. I doubt that's the case here, the margins are higher and the volume is lower on halo products, making it less worth the hassle but I don't put anything past some OEMs when it comes to saving a buck.