I'm asking this as a hypothetical, not directly in reference to Maiden: If I wrote some song lyrics in a vacuum, then later discovered they are eerily similar to another song already written/published, am I liable for plagiarism? And if yes, does that mean that I should be constantly Googling lyrics by other bands to make sure my work is completely original? The same question goes for music. If I write a riff then find out later that another band has a similar riff? The opening riff to Wickerman sounds very similar to Running Wild by Judas Priest. Should Priest have sued Maiden? And how can you possibly prove that a band actively/intentionally stole your work?