Since the authority of retaining sin occurs within Confession, which is under the seal, their can be no public evidence. But I can say that the priests today exercise this authority just as it was clearly given in the Bible. Do you have any evidence that this authority that the Bible says was given to the Apostles was latter taken away?
HMMMmmm... is there PRIVATE evidence?
Has any priest you've ever had contact with said, privately to you, "I just retained Joe Blow's sins."?
The other alternate is that your OWN sins have been 'retained'.
So; which is it?