The criterion was essentially that anyone who was a citizen prior to 1940 or the descendant of such a citizen was granted citizenship. This would exclude those who immigrated during the Soviet-era and who had no prior connection to the Baltic states. Naturalization is possible, but it requires quite an in-depth knowledge of Estonian. Russia has been quite vocal about Russian minorities. Don't know if issuing 116,000 new citizenships over night would be the best tack to take.

I'll have to profess ignorance in the subject matter, but from my understanding Lithuania actively tried to minimize immigration, whereas Estonia and Latvia did not (thus explaining Lithuania's comparatively small Russian minority compared to the other two Baltic states).

And why wouldn't Kaliningrad have a significant Russian population? It is in Russia, after all...

"The basis of optimism is sheer terror" - Oscar Wilde