I don't really understand your question. It looks to me as if you want
<xsl:for-each select="Issue/IssueHistory_CreationDate">
<String><xsl:value-of select = "substring-before(., 'T')"/></String>
</xsl:for-each>
But you make it seem a lot more complicated than that.
Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference