The main thing which should be explained here, is what about the words which were not documented? what about them? Shortly, some words can be created using verbal endings which change the meaning of a word. The best example is the ending "(ǝ)ш" which makes a verb a noun, a documented example of this is ам 'eat' амǝш 'food'. However, some names and theological concepts can't be made using documented elements. And these words were loaned, from Russian because that is what the last Kamasins were already doing, and that would have happend if they never died. However to note, these words are mainly Geographical names, Theological concepts, Inventions that came later and science related. Also animals which the Kamasins never saw and didn't have names for.
NOTE: this is not just Russian with Kamassian words, as a proof you can check how much is documented of the language in the links tab.
We have a huge book by K.Donner and many recordings from Klavdya Plotnikova, who was the last native speaker of Kamassian.