No, you are confusing relative time, with transit time (i.e. the time it takes for the information to reach you).

Relative time is a real thing, certainly and messes with the idea of simultaneous.

But transit time is not that. We and the supernova are more or less in the same frame of reference (we are not accelerating relative to one another, and there isn't much relative velocity difference either).

And because of that it is correct to say it happened xxx years ago.

Is that correct? Let's say Bill was born here on Earth on August 26, 2011, "at the same time" astronomers first detected this supernova. On Earth, we observe Bill's birth and the beginning of the supernova to be simultaneous events. However, isn't it true that an observer at the supernova (presuming he could survive) wouldn't agree that Bill's birth and the supernova were simultaneous, would he?

> On Earth, we observe Bill's birth and the beginning of the supernova to be simultaneous events.

No, that is incorrect. We observe that the light from the supernova reached us now, yes. But we are well aware that it actually happened long ago.

Both us and the distant observer agree about the order and relative timing of the events.

It's only when we are not in the same frame of reference that we would disagree, and that is not the case here.

He would because he knows how fast information travels.