I love getting notifications to old threads I'VE posted, as well as threads I've commented on. Sometimes they regarded a project I wanted to do and forgot about, or sometimes I still have issues with something and love new ideas. and -- if it's a compliment on something I've made it's never too late to receive that!
So in my opinion post away! If you want to ask some individual in the thread something it's best to PM them as they may have unsubscribed from that thread or may no longer be a member of QB. I like the idea here to give them a link to the thread you are PM'ing about.