From Site Rules & Guidelines:
19. Regarding 'necro-posting', understand that a necro-post occurs when a forum user replies to a topic which has not had a reply for more than 3 months where the reply in question does not or very minimally contributes to the relevant discussion. If the reply does in fact contribute to discussion, it is not a necro-post. This is in actuality encouraged, as it promotes use of the search function to find topics. If a necro-post does occur, do not further reply to the topic lamenting the necro-posting -- instead, contact community staff to deal with the issue.
From Site Rules & Guidelines:
19. Regarding 'necro-posting', understand that a necro-post occurs when a forum user replies to a topic which has not had a reply for more than 3 months where the reply in question does not or very minimally contributes to the relevant discussion. If the reply does in fact contribute to discussion, it is not a necro-post. This is in actuality encouraged, as it promotes use of the search function to find topics. If a necro-post does occur, do not further reply to the topic lamenting the necro-posting -- instead, contact community staff to deal with the issue.