Aging 4 Bucket report gives variance in total numbers with every run

Hi

Has anyone come across a variance amount in the seeded Aging 4 bucket report .. the users are complaining that each time they run the report on a given date  there is a slight variance in the final total numbers..

I would assume if you run them on different dates the data could change but withing the same day using the same parameters there is a variance found in every run. we do not know which numbers to believe and it required for the quarter end

Thanks
Meg