I stumbled upon this song while doing research on the 80 Years War.

Is this song authentic?

If it is authentic, how was it preserved and was it used in the 20th century in the same way as "Wir sind des Geyers Scwarze Haufen"?

It mentions approaching Bergen op Zoom from Gelderland - am I right to suppose that these Landsknechte were in service of the Spanish?