The easy solution would be to add something in the original thread, which will bump it back up to the top. The problem is the speed with which new posts come in, which pushes things down the list. I do often look out for unanswered threads to try to ensure that most get an answer. However, I'm not sure that restricting posts would be a viable option, because it would make it impossible for threads to develop into discussion, which some do, and would also restrict answers to people who have recognised teacher status, which would exclude visiting teachers, native speakers and advanced students who can answer the question. However, let's see what others say.
BTW, going back to the original question, I would have given the same answer as the person who originally answered.