That's correct. The banned extremist material was actually seized by customs before it was technically imported. The JWs ran numerous articles on this criticizing the Ministry of Justice for seizing the material.
I'm not sure. Have JW's tried to import literature into Russia after they had been declared as extremist? Or is it that Russia blocked the shipment, sent it to the experts and then declared them as extremist?
On jw.org,
On July 14, 2015, Russian customs officials took an unprecedented step against Jehovah’s Witnesses by denying importation of the New World Translation of the Holy Scriptures, published by the Witnesses in the Russian language. Since March 2015, Russian authorities have stopped all shipments of the Witnesses’ religious publications, even though none of the literature intended for import is banned in Russia.
https://www.jw.org/en/news/legal/by-region/russia/russia-blocks-bibles-20150721/
The timeline of the literature seizing done by Russia:
https://www.jw.org/en/news/legal/by-region/russia/censorship-russian-bibles-literature/