As per my explanation in the other reply, what happens when a 30 month old track suddenly posts is: someone hears it on Open Mic / The Rack, then awards it that final heart that held the algorithm back from posting it.
Site is silly like that. What posts is determined by an algorithm. It works mostly like this:
Positive influences on a track's likelihood to post include: the number of hearts, the number of unique hearters, age of the track (since upload), low popularity of the tracks genre (probably: Pop posts hardest, Experimental easiest). Of negative influence is the amount of tracks by the artist that posted before: the more tracks they have had posted, the harder it gets for a next to post.
DECAY