Using preceding-sibling

I think I'm missing something when attempting to use preceding-sibling,
because it's not working for me.

My data is structure like so:

<!--********************************************** -->

<TOP>
  <RANDOM1>...</RANDOM1>
  <RANDOM2>...</RANDOM2>

  <PRODUCTS>
     <PRODUCT>
          <ID></ID>
          <NAME></NAME>
     </PRODUCT>

     <PRODUCT>
          ...
     </PRODUCT>
  </PRODUCTS>
</TOP>

<!--********************************************** -->

If I have an <xsl:template match="PRODUCT"> template element, how would
I go about writing out the value of the SKU for the preceding node?  I'm
trying to do something like this, but I'm coming up empty:

  <xsl:value-of select="preceding-sibling::SKU"/>



Any help would be greatly appreciated.......... TIA!

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