Discussions over the weekend led to a meeting today in which we thrashed out some of the issues, and we're half-way to a new plan; the immediate requirement was to investigate the cases where there is a sale to a JC buyer between the start date of the custodian activity and the actual sale of a property by the custodian. For the record, the quick-and-dirty XQuery to answer this question is below, along with the answers. It's clear these cases are not edge cases we can ignore; there's a definite pattern here.

let $baseDir := 'file:///home/mholmes/WorkData/history/stanger-ross/landscapes_of_injustice/svnrepo/trunk/xml/',
$startDate := xs:date('1942-03-04'),
$vanDbFile := concat($baseDir, 'landscapes_live_current_lotBased.xml'),
$mapDbFile := concat($baseDir, 'landscapes_mapridgelive_current_lotBased.xml'),
$dbs := (doc($vanDbFile), doc($mapDbFile)),

$custSales := distinct-values(($dbs//title[hasCustodianSeller != '0'][@isNominal='false'][not(matches(effectiveDate, '00'))]/@id))

for $t in $custSales
let $title := $dbs/descendant::title[@id = $t][1],
$tDate := xs:date($title/effectiveDate),
$lotIds := $title/lotsForTitle/lot/@id,
$targets := $dbs/descendant::title[not(matches(effectiveDate, '00'))][lotsForTitle/lot/@id = $lotIds][someOwnersJapanese != '0'][xs:date(effectiveDate) lt $tDate and xs:date(effectiveDate) gt $startDate]

return if (count($targets) gt 0) then concat('Title ', $t, ' has JC purchases in the key window: ', string-join(distinct-values($targets/@id),  ','), '
') else ()

 Title 1034 has JC purchases in the key window: 1111,1159,1160
 Title 1701 has JC purchases in the key window: 1805,1807
 Title 2926 has JC purchases in the key window: 2963
 Title 5323 has JC purchases in the key window: 5379,5423
 Title 5460 has JC purchases in the key window: 5502
 Title 3799 has JC purchases in the key window: 1172
 Title 4113 has JC purchases in the key window: 4192
 Title 4640 has JC purchases in the key window: 4708
 Title 5068 has JC purchases in the key window: 5122,5123
 Title 6453 has JC purchases in the key window: 6456
 Title 6605 has JC purchases in the key window: 6607
 Title 6649 has JC purchases in the key window: 6661
 Title 29141 has JC purchases in the key window: 29144
 Title 29329 has JC purchases in the key window: 29278