As far as we know the Needler hasn't been upgraded throughout the war, it's been the same thing. In gameplay is is a bit different looking and has different amout ammo etc but is always the same weapon, designated the same (T-33).
No referrence book refers it being modified over the years, neither Halo wiki assumes the gameplay differences are in-universe differences (if they did, they would have to assume the human weapon's ranges were like one-tenth of real weapon ranges).
So, i don't buy it really.
They should have just kept the Reach firing sound in Halo 4, the new one doesn't sound "crystalline" (it is more like automatic stapler, not deadly at all)... which is why i wasn't displeased they used the old sounds in FUD.