Problems with <productnumber>

I am using xsltproc to make HTML output with Docbook V4.5 DTD and Docbook V1.74 XSL style sheets.

My book has the following structure:

<book id="bookFRNA418eg">
<bookinfo>
<title>VISUAL DIAGNOSTICS</title>
<productnumber>PN</productnumber>
<releaseinfo>Rev A</releaseinfo>
<copyright><year>2009</year><holder>FRA</holder></copyright>
</bookinfo>
<toc></toc>
&chapterFRNA1102;
</book>

When I look at my output I get :

        VISUAL DIAGNOSTICS
        Rev A

        Copyright © 2009 FRA

I would expect to see the productnumber, PN, rendered somewhere.  Am I doing something wrong?  I get this for both chunked and unchunked HTML.

I even tried adding the following to my customization:

<xsl:template match="productnumber" mode="titlepage.mode">
  <xsl:call-template name="paragraph">
    <xsl:with-param name="class" select="local-name(.)"/>
    <xsl:with-param name="content">
      <xsl:apply-templates mode="titlepage.mode"/>
    </xsl:with-param>
  </xsl:call-template>
</xsl:template>

I thought if I borrowed from the logic for releaseinfo it would make a difference.  It did not make a difference.

Does anyone have any ideas for what I could try next?

Daniel Merchant
FANUC Robotics America