You can just link the new development in an ongoing story that's already on the front page, just like you did. The alternative would be a second front page thread which splits the discussion and is worse all-round.
Edit: Wanted to respond to the top-level comment but you get the point.
There is mod commentary on 'people might miss things because of the title' as well, it's mostly 'it's ok for people to click through the story or thread to figure things out' and that's also a fairly longstanding 'how HN works most of the time' thing.
https://hn.algolia.com/?dateRange=all&page=0&prefix=true&sor...
The operating assumption here is that people are smart enough to follow the developments in the story themselves - in the the thread and outside.