memory - What do letters and numbers in DDR2 description/designation/notation line mean?

E.g. Samsung 2GB 2Rx8 PC2-6400S-666-12-E3.

According to https://en.wikipedia.org/wiki/DDR2_SDRAM#Chips_and_modules :

• PC2 - DDR2


• 6400 - theoretical bandwidth in MB/s, corresponds to base frequency (6400 corresponds to DDR2-400)


• S - SO-DIMM

What are the others? 666-12 looks like timings, E looks like speed class from the same table @Wikipedia (corresponds to part of the timings), what is 3 and 2Rx8, I've no idea.

(The reason for asking is to find out which of these letters and numbers must match for the modules to be able to run in Dual Channel mode w/o slowing each other down. I still wish to know the meaning of the description though.)

EDIT: I've looked though the suggested duplicates, namely: RAM Part Numbers - Meaning?, How do I interpret the specification of memory (RAM)?, Meaning of last 4 digits in a Samsung RAM memory stick, How can I tell what RAM will fit my computer? - and none explains this particular designation.