This XSLT will take a list of PIDs, turn them into file names, and then look at those EAD files and pull out the genreforms.

Pull655s

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
      xmlns:xs="http://www.w3.org/2001/XMLSchema"
      exclude-result-prefixes="xs"
      version="2.0">
  
  <xsl:template match="/">
    <xsl:for-each select="document('PIDsforEADs.xml')/record/pid">
      <record>
      <xsl:variable name="PID" select="."></xsl:variable>
      <PID>
      <xsl:value-of select="$PID"></xsl:value-of>
      </PID>
      <xsl:variable name="doc">
        <xsl:value-of select="concat($PID, '.xml')"></xsl:value-of>
      </xsl:variable>
      <xsl:for-each select="document($doc)//genreform">
        <term>
        <xsl:value-of select="."/>
        </term>
      </xsl:for-each>
      </record>
    </xsl:for-each>
  </xsl:template>
</xsl:stylesheet>