The idea that there is one single meaning, unchanging through time, and somehow crouching in the terms of any folk or trad blues song waiting to be uncovered by those who can crack the code is arguably naïve. Yes, you can draw on your knowledge of contemporary culture and on the accounts of particular singers and their thoughts when they sang it. You can form a theory on that basis. Interesting to do. But who is to say one singer speaks for all the rest? I'm partly with UK folklorist David Atkinson, who discusses this sort of point in connection with ballads on this, on this sort of thing. His work is worth looking up. As this thread shows, lyrics are open to interpretations.