Contemporaries thought Bestuzhev and Marlinskii were two different people
Three things I want to remember from the early chapters of Lauren Leighton’s Alexander Bestuzhev-Marlinsky:
1. He mostly signed his works Bestuzhev before his arrest (with one instance of Marlinskii), and Marlinskii after; contemporaries didn’t realize it was the same writer when Marlinskii began to make a name for himself.
2. After the failure of the Decembrist uprising, Bestuzhev-Marlinskii promptly cooperated with the authorities and gave evidence against his friend Ryleev (while trying to protect others, like his brothers). This led to softer treatment than others received, including the chance to write again. He and Ryleev may have agreed in advance that he would put the blame on Ryleev, who wanted martyrdom and was probably doomed anyway. Part of the evidence for this theory is that he never seemed to feel guilty about Ryleev in his personal letters.
3. As a critic he wasn’t just a civic-minded forerunner of Belinskii, Chernyshevskii, Dobroliubov et al. (as Soviet critics used to emphasize), but also one of the most typical Romantic critics in Russia, who specialized in issues of language and style. He attacked Katenin’s linguistically incorrect view of the relationship between Russian and Old Slavic.
Meanwhile, in my Pisemskii novel, a provincial poet who admires Kukol’nik criticizes Pushkin’s prose, and his opponent in the argument says that, well, he likes Marlinskii, so what can you expect (Men of the Forties, part 3, chapter 12).
XIX век 
All fascinating tidbits! Do you know when people started realizing they were the same person?
Leighton: “The Soviet Academician Mikhail P. Alekseev has examined the evidence relating to this situation and has rightly concluded: ‘It is necessary to realize that the metamorphosis of Bestuzhev into Marlinsky remained the secret of publishing and journalism circles. For the ordinary readers of the epoch, Bestuzhev disappeared forever from literature in 1826; to the readers of the new generation, who knew and loved Marlinsky, the name of Bestuzhev was unknown.’ Thus, regardless of what name is used, it must be remembered that Bestuzhev preceded Marlinsky, and only later in the nineteenth century did the identity of the two become generally known” (30). There may be more detail in Alekseev; the citation is M. P. Alekseev, “Legenda o Marlinskom,” Etiudy o Marlinskom (Irkutsk, 1928), p. 11.
And since you’re here, Hat, here’s another sentence you might like: “One winter he [Bestuzhev] shaved his head bald to prevent himself from seeking company and used this interval to study several languages and literatures” (29).