"Experimental" does not necessarily mean placebos will continue to be administered. If what you say is true, are the participants--those receiving the injection AFTER the Emergency Use Authorization was issued--being INFORMED that they may or may not be receiving a placebo? I've not (officially) heard that the post-EUA research phase is placebo-controlled (other than by those who received the placebo prior to the EUA and do not go on to receive the actual vaccine post-EUA). Do you have a link?

That would violate the principle of informed consent. Well intended or not, beneficial or not, it would not be right. I don't find humor in tricking people. People need to be given accurate, truthful information in order to make wise decisions.