If you scour the extremely helpful Asian Serial Number Guide (a product of the exceptional T-Mar) you might do better than me to learn the secrets of identifying mystery frames, but I'm still a dullard with all that!
However T-Mar mentions a number of brands associated with Miki production of frames, also spelled with two "ks" Mikki and NOT SURE if that's the same or two different mfgs. (including a few from Europe which hardly ever crop up in NorAm) and among these are:
Sakai
Sekai (not the same as Sakai but both sold in Canada)
Norco
Raleigh
SR
Sanwa
Shogun (Mikki)
Specialized
Centurion (another spelled Mikki)
Motioncraft
Bontecoe (NL)
Faglum (Sweden)
Union (NL)

I may have missed some but you can search yourself:
Asian Serial Number Guide

And if SOMEbody can streamline or explain the baffling "encoding of the code" {what the hell is S(1), Y(1), etc. there is no "key" to any of these I can find} it sure would help an idiot like me!