I don't see why the Voight-Kampff test is needed at all...

In the movie, the police chief goes through all the available data of the replicants: their names (Pris, Zhora, Leon and Roy), their photos and their "DOB". Yet, at the beginning, Leon is shown taking the test. In Tyrell Corp. of all places - shouldn't they have the data on all the manufactured replicants? Roy and co. did not even bother to even change their names! So when Leon is tested, why do they need this needlessly convoluted procedure when a simple photo would be enough to ID the guy?

Also, if name and photo doesn't cut it, there would be a million other ways to create some biometric identification for them. For example their eyes were manufactured by the Asian guy as seen later in the film. So how about a simple retinal scan? Or unique fingerprints? Or something more convenient and more exact than this V-K nonsense?

Is there an in-universe explanation for this?