I agree with you that KYC should be announced at the beginning of the bounty, but maybe  the bounty managers themselves don't know KYC is requires for bounty hunters from the beginning until the end of the bounty.  It's all decided by the developer team that there is a KYC required. I often experienced this, and it doesn't matter in my opinion. The decision in our hand as a bounty hunter, whether we want to do KYC or not. In order to not miss any information related to bounty including KYC, we as bounty hunters have to read frequently any information in main telegram or bounty telegram.