The term "Chuvan language" refers to two completely different languages. Here we will refer to the one related to Yukaghir, which the Chuvans, one of the indigenous small-numbered peoples of Siberia, spoke in the first half of the 19th century. Later, some of the Chuvans adopted Chukchi-type reindeer herding and, as a result, were assimilated by the Chukchi and switched to the Chukchi language, maintaining, however, their ethnic self-identification.
The size of the ethnic group according to censuses is, whenever possible, given separately for representatives of the two Chuvan ethnic groups (the Chuvans as a single ethnic group, whose language was related to Yukaghir, had already ceased to exist by the time of the first census). Also, again, whenever possible, the data is provided on how many Chuvans spoke which language (Russian or Markovian) during that period (it must be borne in mind, though, that the data on language proficiency are largely hypothetical).
The Chuvan language is already dead and Markovian will probably share its fate as all its linguistic features have already disappeared from the speech of the Russian-speaking Chuvans, and its significance as a marker of ethnic self-identification will probably fade away over time.