Helgi Hálfdánarson names the 3 underlying poems, all heathen, which he found in Völuspá: Ásaspá, Mímisspá, Járnviðja. He used metrical rules of poetry to find the original poems on which Völuspá was founded.
(–Maddaman með kýrhausinn, 1962, and 2002.–)
Luckily the original heathen poems did not get lost, so the compilation was not an all-bad accident at all!
For fun: The scholars became so so so jealous when Helgi found what they did not see, that they chose to utter no word, but silence the book to death.
Helgi was a translator of great works, highly held in esteem. He became very old and kept on doing marvellous things for us.