What means the icon key by some threads

I thought after one month after last replay the tread is closed with icon key
I see here old threads without key.


I am not sure, but I think that very old threads will not automatically close after 30 days, and if someone posts to one of those threads, they will continue to stay open unless a human being at Omni closes them manually.

For example, this thread was first posted in 2014, and it is still open despite the most recent post being in October 2022.

I think this usually happens when someone searches the forums for a topic, discovers an old thread, and then contributes to it without noticing how old it is.