I contacted the qlikview support sometime back about the same thing, i was told it wasn't essential to retake examinations for different versions but having a certification on the current version is much better. however the certificate of earlier versions are valid. kind of like oracle certifications... im still running with a 9g certification and its still valid
i attached a brochure they sent me when i contacted them.
There is no lifespan or expiration data for Qlikview certification. Basically qlikview certification questions are based on the real time scenarios, set analysis and related to data modelling etc, so this concepts never change. May be this is the reason there is no lifespan for Qlikview certification.