The reason your first SET Said F3-12800CL9D-4GBNQ is because you bought it in a set (2x2gig).Then you sent 1 stick back for A RMA Then they sent you one(1) stick of ram=1x2gig. so the part number would be F3-12800CL9D-2GBNQ. If you were to order the 16 gig set The order number would be F3-12800CL9D-16GBNQ and so on . they sent you the correct RAM. G.SKILL ROCKS!!
I sent both sticks back at the same time.Newegg said that is how the RMA process works.At least in my situation
The first ram I ordered was listed as F3-12800CL9D-4GBNQ for both sticks, on the ram,and on the box.When I looked in cpuz it stated that it was F3-12800CL9D-4GBNQ. The replacement ram had the same part number on both sticks,and the box. Nothing changed to my knowledge.Then I looked at the specs in cpuz ,and it reads F3-12800CL9D-2GBNQ.
I was really pissed.I'm thinking,first I get bad ram,and now a different part number.I verified this using SiSoftware Sandra Lite 2010c,Speccy,and cpuz.Heres the really weird part.Even though the part number does not match the sticker,I was able to increase the speed of the ram in the bios,and run this ram in dual channel at it's rated speed.The program Speccy indicates I have 4GB Dual channel @800.3 MHz.That tells me its running at 1600MHz.It still says the part number is F3-12800CL9D-2GBNQ,which does not make sense,but everything else checks out.I emailed G-skill to ask the question.Maybe I jumped the gun here and got pissed,but these ram issues are driving me crazy.
Here is a response from a G-skill mod.
The package is 4GBNQ (4 Gigabytes, model NQ), each individual stick is 2GBNQ (2 Gigabytes model NQ), different software packages (and even versions) will identify sticks either individually (1,2,4GB) or by package (generall 2,4,6,8, 12, 16 GB)
Is that the answer.I'm not sure,but it still bothers me to some extent.Why would first set be any different then the replacement. Maybe the manufacturer can answer that question.The ram is running fine,and running at the rated specs after changing timings and speed,