To add to the overall knowledge of Epiphone's SN schema, Lord Summerisle has started building up some info regarding how to decode the new format that doesn't have the leading letter (this started in 2008, it seems). Here's what it is starting to shape up to, based on the assumption that the 5th and 6th digits in the SN correspond to the country of origin:
15 = Qingdao (electric)
16 = Qingdao (acoustic)
20 or 12 = DeaWon? or Unsung China? (still not sure which number corresponds to which factory)
21= Unsung, Korea
My MIK Riviera is SN 080522XXXX, which would suggest that 22 is also a Korean plant.
Cheers