For ribosome, only one and first stop codon matters.
Imagine you're reading a book, until you get to a command saying "now stop reading and go away". And you do. So eventhough there may be furter text in the book, of furter commands saying you to do something, it doesn't matter, because you already stopped and left. That's what ribosome does.
The sequence after THE stop codon is kind of "junk" (in fact it most likely is NOT useless in the organisms, beacuse it may contain regulatory sequences, that may affect translation rate or bind other factors doing various things), but it's not important for he ribosomal elongation of the protein.
Terminator contains stop codon (possibly for every frame there is, just to be sure), poly A signal for the respective type of organism (prokaryotic, eukaryotic). Some may contain expression enhancers. This is just a common building brick of plasmids.
As for the C-tags, there doesn't need to be end exactly after the functional protein domain. There can be some "dummy" amino acids, if they don't affect the function of the tag, they doesn't matter.