<result>
     <xsl:sequence select="key('ANAV-to-BDRY', (NAV_IDENT, NAV_CTRY,

</result>

That must be incorrect because the <result> element is erroneously populated

<result>
     <BDRY_IDENT>...</BDRY_IDENT>
     <BDRY_IDENT>...</BDRY_IDENT>
     <BDRY_IDENT>...</BDRY_IDENT>
     ...  <!-- thousands of them -->
</result>

What am I doing wrong?

At least show us minimal but complete samples to allow us to reproduce
that, without any context for the shown

call it is hard to tell whether there should no match, a single one or
why there would be thousands.