not expected to check for past pronunciations every time Joy but when taking songs from a songbook it can be helpful to know the old pronunciation of a word .I referred yesterday to an Irish song called The Star of the County Down . The song's chorus should rhyme the words "Bantry Bay" with "Derry Quay "   .The modern pronunciatiopn of the word "quay" is "key" so when the band sang "derry key", it sounded out of place.
Another Irish song I can think of mentions Dublin's quays ,rhyming "I can no longer stay" with the words "spring up along the quay". It's important to sing such songs as they were intended to sound imo.

(some knowledge of old pronunciations -what would have rhymed at the time a poem was composed - can help when reading an old poems as well)