Learn Dutch: Niet alleen de akte, maar ook de waarheid was jaren geleden ontdekt. - Not only the deed, but also the truth had been discovered years ago.

The word geleden translates to "ago." Just like in English, where "ago" comes after the time ("years ago"), Dutch places geleden immediately after the duration (jaren). It acts as a time postposition, meaning it always comes after the time word it relates to.

Why is the verb was used here instead of had for "had been discovered"?

In Dutch, the passive voice for completed actions (like "has been" or "had been") is built using the helper verb zijn (to be) rather than hebben (to have). Because this is in the past ("had been"), it uses was along with the past participle ontdekt. If you used had ontdekt, it would mean the truth actively discovered something itself!

There are two subjects mentioned (de akte and de waarheid). Why is the verb was singular instead of plural (waren)?

When subjects are joined by the phrase niet alleen... maar ook... (not only... but also...), the verb usually agrees with the subject closest to it. Since the closest subject here is de waarheid (the truth), which is singular, the verb takes the singular form was.

Is niet alleen... maar ook... a fixed phrase?