The problem with what you're trying to put forward here is that you think this is an interpretation. It's not. A 0-day has a very strict definition.
You can't just choose random words or expressions you don't understand without looking them up and decide they mean something else because you thought they did. Otherwise, the annals of medicine would look very different.
The actual usage is more fluid than that. It wouldn't be a common term if it actually only applied for the first day of every vulnerability being known.
"An attack on a software flaw that occurs before the software's developers have had time to develop a patch for the flaw is often known as a zero-day exploit."
The truth is that even with a strict definition, it is subject to change.
The meaning of a word or term today may not be the same tomorrow, languages evolve with the way people communicate, not with the way they get defined.
0-day is a good example, because people outside the security field only care about whether they're vulnerable or not, not about the intricacies of the term.
How about we all agree that you can't/shouldn't, though? Because taking a contrarian position for no other reason than the fact that you literally can does nothing to advance a discussion.
The problem with what you're trying to put forward here is that you think this is an interpretation. It's not. A 0-day has a very strict definition.
You can't just choose random words or expressions you don't understand without looking them up and decide they mean something else because you thought they did. Otherwise, the annals of medicine would look very different.