The Koga-Miyata frames were built in Japan by Miyata, then shipped to the Netherlands for assembly by Koga. Your frameset is actually a bonded main triangle with CrMo stays and forks. Basically it followed the path laid out by the Raleigh Techniums in trying to combine the best traits of aluminum and steel. I also suspect that there was more than a bit of cost reduction driving things, at is eliminated the need for high paid brazers, the need to mitre tubes, etc. This technology shift followed on the heels on the big Yen revaluation that was lowering the competitiveness of Japanese bicycles. I'm just happy to see that the frame wasn't drewed in the conversion process.