There is also the small fact of other now 'native' groups existing in Russia...
Take for example Russian Baptists ( https://en.wikipedia.org/wiki/Union_of_Evangelical_Christians-Baptists_of_Russia
) who have existed since at least 1867.
and how will the law classify Old Believers? Orthodox, or not?
Here is a brief summary and timeline....which will show, that while there are new groups....there are also a multitude that have been there for longer than you think
The history of indigenous, Russian evangelical Protestantism was anticipated by movements such as the Strigolniki in the 14th century and later in the 16th-18th centuries the Molokan, Dukhobor, to some extent, Subbotniks, and in 19th century Tolstoyan rural communes, who prepared the ground for the movement's future spread. The first evidence on some of the above communes' existence appeared in 16th - 17th centuries. A large number of the above communities emigrated to Canada, the USA and Latin America in 19th and 20th centuries.
The first Russian Baptist communities arose in unrelated strains in three widely separated regions of the Russian Empire (Transcaucasia, Ukraine, and St. Petersburg) in the 1860s and 1870s.
From the information of Christian History Institute, the number of Baptists in Russia significantly grew after World War I. Some Russian prisoners were converted by German missionaries and returned home to preach to others. By 1950, there were an estimated 2,000,000 Baptists in the Soviet Union, with the largest portion in Ukraine.
Many leaders and ordinary believers of different Protestant communities fell victims to the persecution by Communist regime, including imprisonment and executions. The leader of the Seventh-day Adventist movement in the Soviet Union Vladimir Shelkov (1895–1980) spent almost his entire life after 1931 in prison and died in a camp in Yakutia. Pentecostals were given 20-25 year prison terms en masse and many perished there, including one of the leaders of the movement, Ivan Voronaev.
In the period after the Second World War, Protestant believers in the USSR (Baptists, Pentecostals, Adventists etc.) were forced into mental hospitals and endured trials and imprisonment (often for refusal to enter military service). Some were even deprived of their parental rights.
so where do you draw the line of 'don't say anything about your beliefs?'