This is an old thread, but I should clarify that Koryo Saram and Sakhalin Koreans are considered different groups. Sometimes Koryo Saram may be used as an umbrella term for all members of long-established ethnic Korean communities in the areas of the former Soviet Union, and in this sense Sakhalin Koreans will be included.
But in the narrower and (I think) more usual sense, Koryo Saram refers to the ethnic Koreans descending from those who were established in the Far Eastern provinces of Russia before deportation and migration spread them all over the former Soviet Union. The Sakhalin Koreans were brought there by the Japanese when the southern half of Sakhalin was under Japanese control, and were essentially stranded there after the Soviets took over.
The Koryo Saram are mostly from the northern provinces of Korea, while the Sakhalin Koreans are mostly from the southern provinces.
As the Soviet Union falls, many of the Koreans in Central Asia moved to Sakhalin...
There, I think you are confusing Sakhalin with the Russian Far East. As far as I know, much of the movement has been to the Maritime Province around Vladivostok, not Sakhalin Island.