A little comment to that portion of your code:
 <xsl:template name="trimmed-data">
       <!-- pos of first non-zero rebate1 -->
       <xsl:variable name="pr1"
select="count(mystruct/myarray1/myvar/rebate1[. &lt;= 0]) + 1"/>

1) I don't quite get what you are calculating here, what does [. <= 0]
mean, that current node <= 0 ?

2) It looks to me that any non-numeric nodes like <blank>, 'NaN', 'N/A', 'abc'
will break the algorithm. How can we make it a bit more robust ?