With no explanation, label text_A→text_B with either "DON'T KNOW", "NO" or "YES".
text_A: Europeans probably became aware of Greenland's existence in the early 10th century, after Gunnbjörn Ulfsson, while sailing from Norway to Iceland, was blown off course by a storm and sighted some islands off Greenland. During the 980s explorers led by Erik the Red set out from Iceland and reached the southwest coast of Greenland. Even though the region that they found was populated, they subsequently claimed it as their own and settled there, with only minimal resistance. Erik named the island "Greenland" ("Grœnland" in Old Norse, "Grænland" in modern Icelandic, "Grønland" in modern Danish and Norwegian). Both the "Book of Icelanders" ("Íslendingabók", a medieval account of Icelandic history from the 12th century onward) and the "Saga of Eric the Red" ("Eiríks saga rauða", a medieval account of his life and of the Norse settlement of Greenland) state that Erik said that "it would encourage people to go there that the land had a good name"."
text_B: Is it plausible, from this passage, that the ancestors of the Inuit had already discovered parts of Greenland before Erik the Red's voyages
YES.