In DS, with SSE you can paint different parts of the page with ease. So in this case, it can update <form> and <label> separately. So instead of one update the backend fires 2. There is not separate marker or indicator for OOB.

I think it is best seen in examples on DS website.

Neat, I'll give DS a go.

HTMX also has the option of using SSE with an extension [0]. I've used this to update the notifications tray for example. You could probably do it for OPs example too.

[0] https://htmx.org/extensions/sse/