Ask HN and PG: Why can't I "reply to" on old comments?

[spoiledtechie]

I wanted just now to reply to an old comment about a year old and I wasn't able to. I guess you remove replies after a while, but why? Spam? I would love to see people still replying to something I wrote over a year ago.

[mahmud]

Now you got me nervous, I am gonna check on my entire posting history daily, to make sure you didn't reply to me.

[icey → mahmud]

It would be very nice to have some kind of reply notification icon in the header. I'd put it in the feature requests, but that thread is closed :(.

[arfrank]

I believe remembering reading in the arc.news code or somewhere else that comments close after 100 days for all posts. That would probably mean all comments then. I may be wrong though.