Are the lyrics to Panihida lifted largely from individual texts within the Octoechos (like Litourgiya for the most part which seemed to have individual songs mostly be taken from sections of the liturgy of St. John of Chrysostom with additions and modifications) or were they taken from various lines and cobbled together into the individual song lyrics (ie were the lyrics to say Pesn' 1 taken largely from specific sections of the Octoechos or were they taken from various parts throughout the text and put together for the song lyrics?)

I ask because I've found an English text of the Octoechos and so far I've seen various lines scattered throughout the text that seem to resemble the lines in the songs but they don't seem to be concentrated in a particular area unlike the source for Litourgiya's lyrics