First point is that a parameter becomes mandatory if you specify
as="xs:integer" with no default value. That's because the "default default"
value of "" is not a valid instance of this type, so there is effectively no
default, which is the same as specifying required="yes".

Running with -T reveals that the offending call (which doesn't supply a
value for the parameter) is at line 31:

             <xsl:apply-templates select="name" />

In my tests with both Saxon 8.7 and Saxon 8.6.1, it fails on the long source
document with or without the exclude-result-prefixes, and it succeeds on the
short source document with or without the exclude-result-prefixes. The
difference between the two cases is that the short one doesn't contain the
data that causes the apply-templates call on line 31 to be activated.

I couldn't work out from your post exactly how you are suggesting that
exclude-result-prefixes affects the outcome. (It would of course be possible
to construct a stylesheet where exclude-result-prefixes does affect the
outcome, but it would be rather artificial).

Michael Kay
http://www.saxonica.com/