These are great questions. Hopefully someone with actual expertise will answer. I am under the impression that the vesicles from ER and golgi are not usually different molecules but rather are parts of the ER or golgi that are “pinched off” with the protein at the final step; and that there are coat proteins that do tell the vesicle where to fuse or not. The vesicles can be as simple as a micro environment to keep the protein from getting degraded or “read” and acted upon in transit. Especially if they are designed to leave the cell without being read or intercepted?