As far as I know they do the verification of all the documents just before sending the medicals request and after medicals are received, then another round of in-depth verification is done by directly calling the employers as well as universities or through an external agency and then only they will decide on the final approval.
One of my friend in Singapore had mentioned this to me as his employer got two rounds of calls for verification.
However, this may change from location to location.
C Lad