The book was never lost. It was shelved.
Fifty chapters. The entire story from Creation to Sinai, retold by the Angel of the Presence to Moses on the mountain. The fall of the Watchers. The giants. The 364-day calendar the Temple actually kept. The covenants, dated to the year, the month, and the day.
When the Dead Sea Scrolls were opened in 1947, Jubilees sat among them in more copies than nearly every book of the Hebrew Bible. The community at Qumran treated it as scripture. Ethiopia never stopped treating it as scripture. Only the West forgot it.
Somebody chose your table of contents. Read the evidence and decide for yourself.