Yeah, but metre in English doesn't really go by syllables, but by stresses - typically in follk sonmgs you'll find lines with masses of extra syllables put in, sung to the same bit of tune more or less.

Just a random example from a songbook I opened to find a random example - the first lines of three verses of "The Sporting Youth"

Some says I'm foolish and more says I'm wise (10 syllables)

If I would leave my parents and go along with you (13 syllables)

So now we are landed and married we be (11 syllables)

And that's by no means an extreme example. Comic songs expecially will make a feature of sticking in a great run of extra syllables, or removing a few. For example:

A Sailor courted a farmer's daughter
Who lived contagious to the town of Strabane
With loving melody he did besought her
That's she'd marry him, and not forsaek him
Or go with any other kind classification or condition of a man.

And the other thing that goes with that is that the idea that there is one exact tune that goes with all the verses in unaccompanied singing is quite out of keeping with most traditions. Collectors like Cecil Sharpe and Baring-Gould would try and sort out what the "right tune" was, and think that the variations were mistakes. And then you get singers trying to cram the words of all the verses into the same tune. Or rewriting the words so that they fit the tune.