well if you group by user and order by start date, you could do a simple datediff, like:
if datediff("w", {table.startDate}, Previous{table.endDate}) < 52 then
//flag the record
else
//don't flag
HTH
ps, I never remember which order to put the dates in the datediff. I tend to print the results and if it is negative, I reverse the date fields