I find that when I read older poetry, the rhyme scheme is sometimes broken and I assume that the problem comes from changes in pronunciation over time. For example, Poe keeps up a pretty impressive rhyme scheme throughout the Raven but it breaks on the lines:
"Prophet!" said I, "thing of evil!
prophet still, if bird or devil!
unless "evil" and "devil" rhyme. When reading that line aloud, should I try to adjust the pronunciation so that they rhyme? Or is it more important to pronounce words in a way that modern listeners will readily understand?