I am using xslt to transform the below XML file into a hierarchy

<?xml version="1.0" encoding="iso-8859-1" ?>
<TABLE>
<LABS>
<STUDY_ID_OR_NUMBER> 01234 </STUDY_ID_OR_NUMBER>
<SITE_ID_OR_NUMBER> 01 </SITE_ID_OR_NUMBER>
<INVESTIGATOR_ID_OR_NUMBER> 01 </INVESTIGATOR_ID_OR_NUMBER >
<INVESTIGATOR_NAME > Dr. Jones </INVESTIGATOR_NAME>
<SCREEN_ID_OR_NUMBER> 100 </SCREEN_ID_OR_NUMBER>
<VISIT_ID_OR_NUMBER> CYCLE1/DAY1 </VISIT_ID_OR_NUMBER>
</LABS>
<LABS>
<STUDY_ID_OR_NUMBER> 01234 </STUDY_ID_OR_NUMBER>
<SITE_ID_OR_NUMBER> 01 </SITE_ID_OR_NUMBER>
<INVESTIGATOR_ID_OR_NUMBER> 01 </INVESTIGATOR_ID_OR_NUMBER >
<INVESTIGATOR_NAME > Dr. Jones </INVESTIGATOR_NAME>
<SCREEN_ID_OR_NUMBER> 200 </SCREEN_ID_OR_NUMBER>
<VISIT_ID_OR_NUMBER> CYCLE1/DAY1 </VISIT_ID_OR_NUMBER>
</LABS>
<LABS>
<STUDY_ID_OR_NUMBER> 01234 </STUDY_ID_OR_NUMBER>
<SITE_ID_OR_NUMBER> 02 </SITE_ID_OR_NUMBER>
<INVESTIGATOR_ID_OR_NUMBER> 02 </INVESTIGATOR_ID_OR_NUMBER >
<INVESTIGATOR_NAME > Dr. Smith </INVESTIGATOR_NAME>
<SCREEN_ID_OR_NUMBER> 100 </SCREEN_ID_OR_NUMBER>
<VISIT_ID_OR_NUMBER> CYCLE1/DAY2 </VISIT_ID_OR_NUMBER>
</LABS>
<LABS>
<STUDY_ID_OR_NUMBER> 01234 </STUDY_ID_OR_NUMBER>
<SITE_ID_OR_NUMBER> 02 </SITE_ID_OR_NUMBER>
<INVESTIGATOR_ID_OR_NUMBER> 02 </INVESTIGATOR_ID_OR_NUMBER >
<INVESTIGATOR_NAME > Dr. Smith </INVESTIGATOR_NAME>
<SCREEN_ID_OR_NUMBER> 200 </SCREEN_ID_OR_NUMBER>
<VISIT_ID_OR_NUMBER> CYCLE2/DAY1 </VISIT_ID_OR_NUMBER>
</LABS>
</TABLE>

And I want to transform it using this xslt:
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance">
<xsl:output method = "xml" omit-xml-declaration="no" indent = 'yes'/>

<xsl:template match="/">

<GTP xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance" xsi:noNamespaceSchemaLocation="CDISC.xsd">

<xsl:element name="Study">

<xsl:element name="File_Creation_Date_and_Time">
<xsl:text>Need to generate time stamp</xsl:text>
</xsl:element>

<xsl:element name="Model_Version">
<xsl:text>1-0-0</xsl:text>
</xsl:element>

<xsl:element name="Transmission_Source_ID">
<xsl:text>MDS</xsl:text>
</xsl:element>

<xsl:element name="Transmission_Source_Name">
<xsl:text>MDS</xsl:text>
</xsl:element>

<xsl:element name="Study_Name">
<xsl:text> STUDY</xsl:text>
</xsl:element>


<xsl:element name="Transmission_Type">
<xsl:text>I</xsl:text>
</xsl:element>

<xsl:apply-templates select="TABLE"/>

</xsl:element>

</GTP>

</xsl:template>

<xsl:template match="TABLE">

<xsl:for-each select="LABS">
<xsl:variable name="Investigator">
<xsl:value-of select="INVESTIGATOR_NAME/text()"/>
</xsl:variable>
<xsl:if test="not(preceding::INVESTIGATOR_NAME[contains(text(),$Investigator)])">
<Investigator>
<Investigator_ID_or_Number>
<xsl:value-of select="INVESTIGATOR_ID_OR_NUMBER"/>
</Investigator_ID_or_Number>
<INVESTIGATOR_NAME>
<xsl:value-of select="INVESTIGATOR_NAME"/>
</INVESTIGATOR_NAME>
<xsl:apply-templates select="//LABS[INVESTIGATOR_NAME=$Investigator]" mode = "Screen_ID_or_Number" />
</Investigator>
</xsl:if>
</xsl:for-each>

</xsl:template>

<xsl:template match="LABS" mode = "Screen_ID_or_Number">

<xsl:variable name="Screen_ID_or_Number">
<xsl:value-of select="SCREEN_ID_OR_NUMBER/text()"/>
</xsl:variable>
<xsl:if test="not(preceding::SCREEN_ID_OR_NUMBER[contains(text(),$Screen_ID_or_Number)])">
<Subject>
<Screen_ID_or_Number>
<xsl:value-of select="SCREEN_ID_OR_NUMBER"/>
</Screen_ID_or_Number>

<xsl:apply-templates select="//LABS[SCREEN_ID_OR_NUMBER=$Screen_ID_or_Number]" mode = "VISIT" />
</Subject>
</xsl:if>

</xsl:template>

<xsl:template match="LABS" mode = "VISIT">
<xsl:variable name="Visit">
<xsl:value-of select="VISIT_ID_OR_NUMBER/text()"/>
</xsl:variable>
<xsl:if test="not(preceding::VISIT_ID_OR_NUMBER[contains(text(),$Visit)])">
<Visit>
<Visit>
<xsl:value-of select="VISIT_ID_OR_NUMBER"/>
</Visit>

</Visit>
</xsl:if>
</xsl:template>

</xsl:stylesheet>

I am not getting the correct child nodes under the correct branch nodes. The output looks like this:
<?xml version="1.0" encoding="UTF-8" ?>
- <GTP xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance" xsi:noNamespaceSchemaLocation="CDISC.xsd">
- <Study>
<File_Creation_Date_and_Time>Need to generate time stamp</File_Creation_Date_and_Time>
<Model_Version>1-0-0</Model_Version>
<Transmission_Source_ID>MDS</Transmission_Source_ID>
<Transmission_Source_Name>MDS</Transmission_Source_Name>
<Study_Name>PFIZER STUDY</Study_Name>
<Transmission_Type>I</Transmission_Type>
- <Investigator>
<Investigator_ID_or_Number>01</Investigator_ID_or_Number>
<INVESTIGATOR_NAME>Dr. Jones</INVESTIGATOR_NAME>
- <Subject>
<Screen_ID_or_Number>100</Screen_ID_or_Number>
- <Visit>
<Visit>CYCLE1/DAY1</Visit>
</Visit>
- <Visit>
<Visit>CYCLE1/DAY2</Visit>
</Visit>
</Subject>
- <Subject>
<Screen_ID_or_Number>200</Screen_ID_or_Number>
- <Visit>
<Visit>CYCLE2/DAY1</Visit>
</Visit>
</Subject>
</Investigator>
- <Investigator>
<Investigator_ID_or_Number>02</Investigator_ID_or_Number>
<INVESTIGATOR_NAME>Dr. Smith</INVESTIGATOR_NAME>
</Investigator>
</Study>
</GTP>

is it possible in the <xsl:value-of select=""> statement to only select nodes based on other leaves in the branch?

TIA