Ever wonder what happens RMA DDR memory.. Yes they are sometimes returned back or sold on with mixed chips without most if not all users not knowing. Anyone doubt what I'm saying, I have the evidence here from big manufactures, with the memory modules not tampered with, so yes, some brand new memory modules were sold with mixed ram chip. I only know they were doing this in the pass, so I don't know if they are still doing it today with modern DDR4. I have detected this in DDR1 memory modules only, but I'm fairly confident this was going on in DDR2 & DDR3.
If requested I can upload a photo, but it will name & shame a few big company's. AFAIK I have caught up-to three company's with mixed ram chips under the hood, ie heatsink.