Being in "best" when sorted doesn't make a thread immune to locking in the event of "Necro posting". It may not seem like a big deal, but commenting on old threads bumps them up the list, which clutters up the boards with old, irrelevant threads / information.
Keep in mind that we don't lock threads for being generally old, but after an extended period of time has elapsed between replies to the point where conversation is usually forgotten and irrelevant; usually a month.
In the event that a thread is locked for this reason, you're more than welcome to make a thread of your own regarding the same topic as long as it adheres to the Universal Rules.