english original missing
When searching for any keyword using the search box at the top left, obsolete messages containing the keyword in question will show up in the search results the same way current ones do, with no way to distinguish between them from the results list.
You can distinguish them on the translation page itself by the absence of an English original (and in the classic/non-Javascript editor, by the absence of the "In other languages" link at the left), but for most users, this is confusing and clarifies nothing.
I do agree with keeping obsolete messages. They are useful for translation memory purposes if nothing else. But I think it would be good to have some clear way of distinguishing them from current messages, in search results and in the edit pages themselves.