Thanks again to everyone who helped me get my head around this problem. I've
posted my conclusions on my blog (rather than gumming up the list more than I
already have).

In retrospect I may not have presented the problem as clearly as I could have
and hope that the blog post clarifies what the problem was. The good news is
THE PROBLEM WAS SOLVED and I thank all of you for your help. This is one of
the best lists I've ever been on and I hope my grain of sand helps someone in
my situation down the road.

Here's the final key element I ended up with:

<xsl:key
    name="ports-by-ship"
    match="tr"
    use="(ancestor-or-self::tr[count(td) &gt;= 6]/td[1]
        | ancestor-or-self::tr/preceding-sibling::tr[count(td) &gt;=
6][position() = count(.)]/td[1])[last()]"
/>

http://www.tecnotertulia.com/?p=330

Sincerely,

Ted Stresen-Reuter