Yes, 4CY is a different factory. I do not work for HP or either of these companies, so I am not 100% sure, but I believe that 4CY == Inventec Appliance, and CNA == Kinpo Electronics.
We know HP uses both of these manufacturers (They've admitted to using Kinpo, and some of the PDFs in the 20b SDK had engineering drawings by Inventec).
My reasoning for believing this mapping of serial number to manufacturer is as follows:
We know that Kinpo made the HP-35s, and the 35S has a "Regulatory Model Number" molded into the back that reads HSTNJ-KN01, and a serial number beginning with CNA.
My 30b has a serial number beginning with 4CY and a "Regulatory Model Number" of HSTNJ-IN07. My 12c+ looks like the 'unexpected' one and has a 4CY serial number, regulatory model number HSTNJ-IN04. Also, the 30b and 12c+ serial number stickers are the same color and same font.
My 15C LE has a CNA serial number and model number HSTNJ-KN13. Its' serial number sticker doesn't match the 30b or 12c+ ones.
And sure enough, if you look at the picture of the backs of the two 12c+es, you'll notice "HSTNJ-IN04" underneath the multilingual "Product of China" on the 4CY one, and "HSTNJ-KN05" underneath "Product of China" on the CNA one.
Edited: 16 Oct 2011, 9:22 p.m.