Sort on different date format(mmddyyyy) - xslt - sorting

Question

I have a date field in XML which will always be in MMDDYYYY format. I am trying to sort using the date by the following code:
<xsl:sort select="format-date(Date, '[M01][D01][Y0001]')"/>
Need help in resolving.
I have got a clue by calling a function within sort where we can convert this into ISO format. Can we ignore calling the function when Date field does not appear in some XML elements?
Following example shows the input XML as well as XSLT Code:
Input XML:
<?xml version="1.0" encoding="UTF-8"?>
<EmpD>
<PR>
<RType>02</RType>
<Emp>888</Emp>
</PR>
<PR>
<RType>02</RType>
<Emp>889</Emp>
</PR>
<JR>
<RType>01</RType>
<Emp>888</Emp>
<Type>C</Type>
<EDate>05012020</EDate>
<HR>1210148900</HR>
<JobC>Test</JobC>
</JR>
<JR>
<RType>01</RType>
<Emp>888</Emp>
<Type>NC</Type>
<EDate>05022019</EDate>
<HR>1210148900</HR>
<JobC>Test</JobC>
</JR>
<JR>
<RType>01</RType>
<Emp>888</Emp>
<Type>C</Type>
<EDate>05022020</EDate>
<HR>1210148900</HR>
<JobC>Test</JobC>
</JR>
<JR>
<RType>01</RType>
<Emp>889</Emp>
<Type>C</Type>
<EDate>05012020</EDate>
<HR>1210148900</HR>
<JobC>Test</JobC>
</JR>
<JR>
<RType>01</RType>
<Emp>889</Emp>
<Type>NC</Type>
<EDate>05012020</EDate>
<HR>1210148900</HR>
<JobC>Test</JobC>
</JR>
<JR>
<RType>01</RType>
<Emp>889</Emp>
<Type>NC</Type>
<EDate>05032019</EDate>
<HR>1210148900</HR>
<JobC>Test</JobC>
</JR>
</EmpD>
XSLT Code:
<?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" xmlns:ab="test" exclude-result-prefixes="#all" version="3.0">
<xsl:function name="ab:us-date-to-iso" as="xs:date">
<xsl:param name="us-date" as="xs:string"/> <!-- format MMDDYYYY -->
<xsl:sequence select="xs:date(replace($us-date, '(..)(..)(....)', '$3-$1-$2'))"/>
</xsl:function>
<xsl:strip-space elements="*"/>
<xsl:output indent="yes"/>
<xsl:mode on-no-match="shallow-copy"/>
<xsl:template match="EmpD">
<xsl:copy>
<xsl:apply-templates select="*">
<xsl:sort select="Emp"/>
<xsl:sort select="RType"/>
<xsl:sort select="ab:us-date-to-iso(EDate)"/>
</xsl:apply-templates>
</xsl:copy>
</xsl:template>
</xsl:stylesheet>
Desired Output:
<?xml version="1.0" encoding="UTF-8"?>
<EmpD>
<JR>
<RType>01</RType>
<Emp>888</Emp>
<Type>NC</Type>
<EDate>05022019</EDate>
<HR>1210148900</HR>
<JobC>Test</JobC>
</JR>
<JR>
<RType>01</RType>
<Emp>888</Emp>
<Type>C</Type>
<EDate>05012020</EDate>
<HR>1210148900</HR>
<JobC>Test</JobC>
</JR>
<JR>
<RType>01</RType>
<Emp>888</Emp>
<Type>C</Type>
<EDate>05022020</EDate>
<HR>1210148900</HR>
<JobC>Test</JobC>
</JR>
<PR>
<RType>02</RType>
<Emp>888</Emp>
</PR>
<JR>
<RType>01</RType>
<Emp>889</Emp>
<Type>NC</Type>
<EDate>05032019</EDate>
<HR>1210148900</HR>
<JobC>Test</JobC>
</JR>
<JR>
<RType>01</RType>
<Emp>889</Emp>
<Type>C</Type>
<EDate>05012020</EDate>
<HR>1210148900</HR>
<JobC>Test</JobC>
</JR>
<JR>
<RType>01</RType>
<Emp>889</Emp>
<Type>NC</Type>
<EDate>05012020</EDate>
<HR>1210148900</HR>
<JobC>Test</JobC>
</JR>
<PR>
<RType>02</RType>
<Emp>889</Emp>
</PR>
</EmpD>