With accents (as with language generally) it's vital to understand they change over time. We're all familiar with hearing cockney or middle class accents on old British films. They were not putting it on, that's actually how everyone in their neck of the wood spoke at the time.

In modern times the 'r' is disappearing from words like 'brought' - I'd suggest that a majority in the UK now routinely say 'bought,' which used to mean quite a different thing. This is not 'wrong' it's just what happens. Witness the words 'walk' and 'talk' which used to have an audible 'l'. 'Vulnerable' is currently interchangeable between both pronunciations. (Mater still says 'goff' for the scottish game, and sodder for that melty metal).

This has been going on for as long as folk have spoke. Listen to Pete Morton doing Chaucer, and remember that the New England accent has changed less since the Pilgrim Fathers' time than has plain English.

So there is no such thing as 'correct' pronunciation - only pedantic (literally) decisions to impose one random accent on the users of another to imply a social standing.

It's slightly different with TV and radio, because here we are trying to reflect a carefully-derived consensus, but in normal speech - and in song - there are no rules, only better or worse understanding (and projected values).

Tom