If I do understand you correct, you want to use information of one (or all) of the datasets, which are produced by a tabletemplate in one of the bodies, within a meta tag in the pagetemplate.
Let us say, that you want to use the newest value of the column "lastChange" of all datasets in the meta tag date, as long as there are datasets rendered on the actual page.
This here should work:
<meta name="date" content="$CMS_TRIM(level:4)$
$CMS_IF(#global.multiPageParams.data.isNull)$
$CMS_VALUE(#global.page.changeDate.format(set_format))$
$CMS_ELSE$
$CMS_SET(set_changedate,"01.01.1970".toDate("dd.MM.yyyy"))$
$CMS_FOR(dataset,#global.pageParams.data)$
$CMS_IF(dataset.lastChange > set_changedate)$$CMS_SET(set_changedate,dataset.lastChange)$$CMS_END_IF$
$CMS_END_FOR$
$CMS_VALUE(set_changedate.format(set_format))$
$CMS_END_IF$
$CMS_END_TRIM$"/>
If you want to use the value of the first dataset, you just can get the dataset with
#global.pageParams.data.get(0)
changed two typing errors [wrong variable names) - sorry