Snippet to generate data for pasting into spreadsheet:

declare default element namespace "http://www.tei-c.org/ns/1.0";

for $t in //@target[parent::ref[ancestor::xr]]
let $id := substring-after($t, 'm:')
where not(//entry[@xml:id=$id])
order by $t/ancestor::TEI/@xml:id, $t/ancestor::entry/@xml:id
return concat($t/ancestor::TEI/@xml:id, '.xml	', $t/ancestor::entry/@xml:id, '	', $t)