I was thinking on this for a bit -- I think it has a time-out, where after <x> amount of time (above 3 months), it no longer becomes visible to players, whereas GMs can see all of them, no matter their age. I don't know if this is a bug or not, but I'd like to see it changed/fixed, as I have some info in old threads I'd like to dig up.
The pine tree wastes which is perched on the hill,
nor bark nor needles shelter it;
such is the man whom none doth love;
for what should he longer live?