It turns out that matching against only <seg type="n"> misses most of the matches, because entries that haven't yet been processed don't have type attributes. Thus take 2, which finds 670 matches:

declare default element namespace "http://www.tei-c.org/ns/1.0";
import module namespace util="http://exist-db.org/xquery/util";

for $p in collection('/db/moses/')//TEI[@xml:id='lex-suff']//phr[@type='n'][parent::quote]
let $target := normalize-space(translate($p/text()[1], '+-=√‐', '')),
$matches := collection('/db/moses/')//pron/seg[text() = $target]
return
if (count($matches) gt 0) then
concat('*** ', $p/ancestor::entry/@xml:id, ' (', $target, ') [', $p/text(), '] matches ', collection('/db/moses/')//pron/seg[text() = $target][1]/ancestor::entry/@xml:id)
else
concat('    ', $p/ancestor::entry/@xml:id, ' (', $target, ') [', $p/text(), '] has no matches. ')