>>> But why all this turgid code? the whole thing can be written as

>>> <xsl:template match="Account_or_Subaccount">
>>>   <Contract Sub_ID="{Subscriber_Info/@Sub_Id}"
>>>             Org_ID="{Characteristic[@Display_Lable='Organization ID']}" />
>>> </xsl:template>

>>> [is "Lable" spelt correctly??]

Thanks for that improvement! The reason it was done with extreme turgidity is historical: that was the first formulation that (almost) worked. Now I, newbie, can look up the curly-braces. 

And yes, LABLE (and its sibling DISPLAY_LABLE) are spelt that way in the input file.