So for the song to have been recorded back in 1927 means that it is Public Domain.Correct? What does it matter who wrote it? I myself have heard many different versions of it as well a number of verses mixed in from other tunes. To find out the orgional form of the tune is just impossible.
I live in Eastern Kentucky and the reference to Harlan and Hazard has always been clear to me. It was either due to prohibition or the fact that we have dry counties in the state that don't allow the sale of alcohol. Perhaps Harlan and Hazard were the two places (that the author knew of)to get some whiskey or home brew. It does make reference to "get a little brew".
I play music , and jam at festivals all over the place and have heard many different verses to this song. Heres what I can remember:

I'm going on the mountain
Just to see my baby
And I ain't coming back, Lord, Lord
No I aint coming back

This Nine pound hammer
Is a little too heavy
Buddy for my size
Buddy for my size

Roll on Buddy
Don't you roll so slow
How can I roll, Lord , Lord
When the wheels won't roll

Their ain't one hammer
down in this tunnel
that will ring like mine
tha will ring like mine

Rings like silver
Shines Like Gold
Rings like silver
and shines like gold

This ole hammer
well it killed (my buddy/John Henry)
ain't gonna kill me
ain't gonne kill me

You can take this hammer
Give it to the captain
tell him I'm gone
tell him I'm gone

If He asks you
where I've gone to
tell him you don't know
tell him you don't know

It's a long way to Harlan
and a long way to Hazard
Just to get a little brew
just to get a little brew

When I'm long gone
You can make my tombstone
Out of number nine coal
out of number nine coal

I have heard it many ways. These are some of the verses that I remember right now. The subject matter in the verses vary, it certainly appears to be the classic case of many songs mashed together. It happened back then because they didn't have records to learn from. They heard someone sing it and they tried their best to remember it and then they mixed in other verses to fill it up. It was all passed on by playing and singing.
I have researched many songs and am still looking for many songs. It's always the same tale the verses vary from the recordings and what common musicians or balladeers sang. Which makes it all the more interesting, the mystery, the many interpretations.