Before the Oceanic 5 came back in "316," it's hard to believe that there were only 4 Flight 815 survivors left to rescue. 4 out of 48... and one of them wasn't even in the original 48. (Also, admittedly, we don't really know the deal with Claire.) But to hear the ones who left talk about "everyone we left behind," they must've thought they were talking about more than 4 people and a dog.
I thought it'd be interesting to examine how 48 became 4 by breaking it down. This includes only fuselage survivors and the Tailies who came to join them in season 2; the rest of the Tailies would fall under a different list since they weren't ever part of the survivor count, and they can generally be summed up as having all been killed or converted to Otherland. "Survivors of other incidents" like Desmond, Rousseau, Karl, Alex, and Lapidus are not included here. The only mention of non-815ers comes near the end, to reconcile the survivor count to Ellie Hawking's 20 in "Jughead."
So here goes:
48 Starting number (Jack's original count after Gary Troup is sucked into the turbine)
-1 Marshall Mars (died of crash-related injuries, being shot, and being suffocated)
-1 Joanna Miller (drowned)
-1 Ethan Rom (not an actual survivor, later shot by Charlie)
-1 Scott Jackson (killed, presumably by Ethan)
+1 Aaron Littleton (born on Island)
-1 Boone Carlyle (crushed by cargo plane)
-1 Dr. Leslie Arzt (blown up)
-1 Shannon Rutherford (shot by Ana Lucia)
+4 Ana Lucia, Libby, Eko, Bernard (tail-section survivors who joined the camp)
-2 Ana Lucia and Libby (shot by Michael)
-2 Michael and Walt (escaped Island)
-1 Eko (killed by Smokey)
-2 Nikki and Paulo (buried alive)
-1 Charlie Pace (drowned)
-4 Doug, Jerome, two women (shot by mercenaries)
-1 Claire (missing and presumed to be God-knows-where-and-when)
-3 Background survivors (killed aboard freighter when it exploded)
-6 Oceanic 6 (escaped Island)
24 (survivor count at start of season 5; this is where it gets a little confusing):
-2 Locke and Jin not at camp during flaming arrow attack
+4 Juliet, Charlotte, Daniel, and Miles (all not on plane) at camp during attack
-6 Unaccounted for (perhaps explained away in other media)
20 Total number of people at beach camp before arrow attack, according to Ellie Hawking
-11 Background survivors, including Frogurt, Craig, Steve, and Richard (killed in flaming arrow attack)
9 Sawyer, Juliet, 3 Freighties, 2 background, Rose, and Bernard (all survive attack)
-2 Background survivors (killed by Claymore mines)
-2 Add back Locke and Jin, subtract 3 freighties and Juliet
-1 Locke (leaves Island and dies)
4 Sawyer, Jin, Rose, and Bernard. And Vincent.
So that's it. Those 4 were the other Flight 815ers left, and at least two of them had no interest in being found. I suppose we should add back in Juliet and the three Freighties, but they're all dead now except for Miles. So... I think it may be safe to say the O5 got back a little too late. They were barely even lying when they told everyone that no one else from the plane had survived.
Stupid paralyzing spider.