Musing ~ about rhymes

Oscar Mayer bologna song lyrics, from the 1970s:

My Bologna has a first name,

It's O-S-C-A-R.

My bologna has a second name,

It's M-A-Y-E-R.

Oh I love to eat it everyday,

And if you ask me why I'll say,

Cause' Oscar Mayer has a way

with B-O-L-O-G-N-A!!!!

Why don't these words rhyme —> tough, though, cough, through, rough, thoughts?

Yet for some reason these words do rhyme —> pony, boney, Coney [Island], bologna.

I also read somewhere that there is no word in the English language that rhymes with "month."  Can you think of a word to prove that's wrong?