Viva la quince brigada
Viva la quinta brigada

You see the difference? 'Quince' is 'fifteenth' and 'quinta' is 'fifth'. Christy Moore sings audible 'quinta' and 'fifth international brigade' and has it in this version on his website.

Wikipedia (and the DT by the way) interestingly reprints Christy Moore's song and changes both the title and the lyrics into 'fifteenth' without commenting that change. As far as I can see wikipedia is historically correct and Christy Moore is wrong.

The two songs are completely different. I interpret Christy Moore as quoting (rather misquoting) the old song title in his new song.

Wolfgang