Buryat shamanic practice west of Baikal was suppressed in the 1920s and 1930s along with the Buddhist establishment east of it. Practitioners were arrested, ritual grounds were destroyed, and the transmission that carried invocations and genealogies from one specialist to the next was broken inside a single generation. When Buryat religion could be studied again after 1990, much of what could be recovered in the field was recollection at second or third hand.
The collected works of Khangalov, published in three volumes at Ulan-Ude in the 1950s and 1960s, are therefore not one source among several. For a great deal of western Buryat practice they are the record. His notebooks preserve texts in the language they were performed in, from people who were performing them, before anyone had an interest in presenting the tradition either as a national inheritance or as a superstition to be cleared away.
He died in 1918, before the suppression began, which spared him what happened to Ksenofontov and Dorzhiev and left his papers intact. The contemporary revival of Buryat shamanic practice draws on his volumes directly, which puts an ethnographer's notebooks in the unusual position of being a source of authority for a living practice rather than a description of a dead one. Whether that amounts to continuity or to reconstruction is argued about in Buryatia itself, and it is not an outsider's question to settle.