Now, I had a older iMac that I just replaced just recently and I had bought Apple co-branded memory several years ago to upgrade the existing memory and the factory installed memory and the branded memory had a lable with a Apple part number and an Apple logo on it for BOTH factory installed AND what I bought from Apple in the Apple box. Now, that was a few years ago and for the time period since Macs first hit the market, that's how Apple did things. Of course Apple doesn't mfg their own memory. DId i mention that they mfg it? NO. But they do factory install it, and they do sell memory upgrade kits in boxes with their name on it, or at least they used to.
Now, Apple might have changed policies on things because when i always dealt with Apple AppleCare or the Apple Warranty, if the product came in with non-Apple branded memory, the user would have to take out the 3rd party memory and install Apple branded memory in the computer before they could service it. The reason is that Apple just doesn't want to work on a part that was originally supplied BY Apple or sold by Apple with the Apple logo on it.
Now, they've used various memory suppliers over the years and that is just dependant on who can supply what they need that meets their specs, which are quite stingent. They have their memory tested to much higher extremes in terms to obtain better reliability.
I've dealt with third parties over the years, Kingston, OWC, MacMemory, Crucial, etc. and what I've found is that memory supplied by Apple or bought afterwards that had the Apple branding on the box was far more reliable. I never had a problem with it. I would have problems with memory that I bought from other suppliers whether it was Crucial (even though the original memory was supplied by Apple and was also co-branded Crucial), etc. etc. It usually took about a year before the 3rd party NON-Apple co-branded memory before it would fail.
Either way, I won't ever recommend buying additional memory from a 3rd party if the computer is under warranty since Apple Support people might not touch it until the memory is replaced, but obviously go to Apple Support personnel and ask them directly how they handle break/fix with memory. It, from a logitstics standpoint is better to go with Apple branded parts bought directly from Apple, especially if it is covered under warranty or AppleCare warranty. Since one person was discussing a computer that's less than a year old, I will only suggest buying Apple memory instead. What they do is their decision.
I was merely mentioning this because on my older iMac which i just replaced, had a Sticker with an Apple part number and Logo in addition to the OEM mfg information, so this is a new circumstance. If you want me to prove it, I have to track down my friend that has my old system and pull out the memory and take a photo of it, but please trust me. It does have an Apple logo and part number on it.
Now, I just bought a 27inch iMac and shut it down and pulled the memory and yes, it doesn't have any other markings than the OEM mfg markings. so what it appears to be is a change in Apple not using an Apple logo/part number sticker and this is something that is recent as far as how Apple does things. SInce I don't work for Apple I can't comment on their policies.
Now, in terms of what is more reliable, I would go with Apple co-branded parts for memory and hard drives that are purchased through Apple that come in an Apple Box. Yeah, they might be more expensive, but I have had ZERO problems with Apple co-branded memory and hard drives and I've been using Apple products since the beginning.
If the product is not covered under warranty, if you want to go with cheaper 3rd party stuff, go right ahead, but don't blame anyone if it doesn't work as reliably, if it does, great!