Complex sentence: The prototype for this were similar bulletins by repressed groups that had been in circulation for some time, such as a Baptist periodical, which had been published since 1965, and specifically the informational bulletin of the Crimean Tatars, which had been established in 1964.
Split into simpler sentences: The prototype for this were similar bulletins by repressed groups that had been in circulation for some time. These included a Baptist periodical, which had been published since 1965, and specifically the informational bulletin of the Crimean Tatars, which had been established in 1964.