In the main report, group by client and insert a subreport into the client group header or footer. Link the sub to the main report on client and on the main report report end date (Let's assume it is a parameter {?EndDate}). In the sub, go into report->selection formula->record and change the selection formula so that the date selection looks like this:
{table.date} <= {?pm-?EndDate} and
{table.clientID} = {?pm-table.clientID}
Then still in the sub, go to report->selection formula->GROUP and enter:
{table.date} = maximum({table.date})
This will return the most recent record for the client that is on or earlier than the main report end date.
-LB