Tried that with no luck.

This probably means no parameter was passed to the template.
You'll have to have a
 <xsl:apply-templates select="...">
   <xsl:with-param name="report_name" select="'foo'"/>
 </xsl:apply-templates>
which selects a BeginEndDate to match.

In your case either you never passed a parameter to any
template, or there was a default template interfering.

It is best to learn how to use template parameters with
small test cases rather than full blown production code.

If you want to use a stylesheet parameter, define the
<xsl:param> as child of <xsl:stylesheet>. You still have
to pass the parameter value from the outside using a processor
specific mechanism.