Learn German: In der Truhe lag ein Buch, dessen Titel unentdeckt blieb. - In the chest lay a book whose title remained undiscovered.

Using bleiben (here in its past tense, blieb) with a past participle starting with un- highlights a continuous state of non-occurrence. While a standard passive like wurde nicht entdeckt simply states the fact that it wasn't discovered, unentdeckt blieb emphasizes that this state persisted over time (it "remained undiscovered").

Could I say blieb nicht entdeckt instead of unentdeckt blieb?

Not naturally. The verb bleiben links to adjectives or words acting as states. By adding the prefix un- to the past participle entdeckt, you turn it into a true adjective describing an ongoing condition (unentdeckt). Using nicht entdeckt with bleiben sounds wrong because entdeckt on its own feels like an action verb trying to form a passive, which requires werden, not bleiben.

Why is the word dessen used here?

dessen is the genitive relative pronoun for masculine and neuter nouns. It refers back to the neuter noun ein Buch and indicates possession, functioning exactly like the English word "whose": "a book whose title".

Why is this sentence using the simple past (lag, blieb) rather than the conversational past (hat gelegen, ist geblieben)?