Unique node and delimiter concatenation

Hi ,
I getting struck with border condition in the below xslt when i am
trying to concatenate with "," "and " while finding unique node based
on the condition.
Can any one suggest me how I could over come this ?

My xml looks like
<LINE_ITEMS>
<LINE_ITEM>
<PRODUCT_NUMBER>1</PRODUCT_NUMBER>
<CUST_MSG>Y</CUST_MSG>
</LINE_ITEM>
<LINE_ITEM>
<PRODUCT_NUMBER>1</PRODUCT_NUMBER>
<CUST_MSG>Y</CUST_MSG>
</LINE_ITEM>
<LINE_ITEM>
<PRODUCT_NUMBER>1</PRODUCT_NUMBER>
<CUST_MSG>Y</CUST_MSG>
</LINE_ITEM>
<LINE_ITEM>
<PRODUCT_NUMBER>2</PRODUCT_NUMBER>
<CUST_MSG>N</CUST_MSG>
</LINE_ITEM>
</LINE_ITEMS>
and
my XSLT the same
<?xml version="1.0"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="html" />
<xsl:key name="getUniqueData" match="PRODUCT_NUMBER" use="."/>
<xsl:template match="/">
<xsl:variable name="itemsOfthisProduct" select="//LINE_ITEM"/>
<products>
<xsl:for-each select="$itemsOfthisProduct/PRODUCT_NUMBER[generate-id()
= generate-id(key('getUniqueData',.))]">
<xsl:variable name="warn"
select="following-sibling::*[contains(name(), 'CUST_MSG')]"  />
<xsl:if test="$warn='Y'">
<xsl:value-of select="."/>
</xsl:if>
<xsl:if test="position() &lt; last()-1 and test=$warn='Y'">
<xsl:message>less than</xsl:message>
<xsl:text>, </xsl:text></xsl:if>
<xsl:if test="position()=last()-1 and test=$warn='Y'"><xsl:text>and
</xsl:text></xsl:if>
<xsl:if test="position()=last() and test=$warn='Y'"><xsl:text>.</xsl:text>
</xsl:if>
</xsl:for-each>
</products>
</xsl:template>
</xsl:stylesheet>

My expected out is
<products>1 and 2.
depends on the CUST_MSG value I need to concatenate "," and respective
locations.

Am facing some border condition it is failing to produce the desired output.
Please help.
Regards,
Senthil