you can use a running total
name = whatever
field to summarize=ClearQuest.id
summary type = distinctcount
evaluate = use a formula
{table.review_date} in Minimum({ClearQuest.action_history_timestamp}) to Maximum({ClearQuest.action_history_timestamp})
or
{table.close_date} in Minimum({ClearQuest.action_history_timestamp}) to Maximum({ClearQuest.action_history_timestamp})
reset=never (for a grand total - you can reset on group level if you want group totals)
place in the report footer (or group footer for group totals)
You can also use a variable formula if you prefer.