I would think it would be hard to get a flight review and not know it. Your logbook will have sometime along the lines of:
I certify that (First name, MI, Last name), (pilot certificate), (certificate number), has satisfactorily completed a flight review of section 61.56(a) on (date).
J. J. Jones 987654321 CFI Exp. 12-31 -05
at the completion.