The Prisoner is the second song in the Maiden album canon to start with "The", which is 'specific'. It is outclassed in that regard two tracks later by The Number of The Beast. As you point out, it is also a B-side to The Clairvoyant. Maybe @RTC is wrong and I am right after all?...
I'm sorry, I got what you meant the first time. I just meant that when I went through the songs, I hadn't thought of that criteria.