I feel drawn to this thread, like a
dragon to a dwarf-hole!
I think that the suggestion of
Huan's that it is more plausible that
orcs are immortal than that they pass down
tales from one generation to the next is wrong, particularly if the implication is that Shagrat and/or Gorbag
remember the Great Siege. I certainly see nothing in the text to suggest that they are speaking first hand of
events they recall.
What we do get is an insight into
orc society, which suggests that they do indeed talk and reminisce about the past. We know the murder rate is pretty high amongst orcs, and that they don't do compassion in a big way, but it is not the case that they are stupid, don't talk to each other, and don't have a collective identity. On the contrary, they appear capable of maintaining continuous social orders (of some kind - particularly when directed by a greater power) for many many years. This means they are capable of self-organisation, talking to each other, and therefore (as with any society) telling stories that shape their identity and self-image. I see no reason at all to think they might not have stories about the past (even if their historical record might not accord with that as told in
Rivendell!).
I think the clearest evidence we have of the life-span of orcs is the case of
Bolg who led the orcs into the
Battle of Five Armies (TA2941), who's father was slain by
Dain Ironfoot in TA2799. This means he was at least 142 (unless someone has a theories about
orcish embryo freezing, or freakishly long gestation periods!

).
My own feeling is that orcs might have the
capacity for long life, but due to their 'life-style' not many survive that long. Perhaps too, some have more the longevity gene than others. But I'm not sure there would have been any maia-orcs left in the TA. We know there were originally many
Maia drawn into
Melkor's service in the Beginning. But how many of these would have survived the many
battles Melkor fought?