Can we figure it out from this? The manned trip to Mars takes 124 days ~= 4 months (possibly the unmanned trips are faster). There are "a total of fourteen unmanned missions", "start to finish, including supply missions, a Mars mission takes about three years", and for the MAV "it takes twenty-four months to fill the tank" (later we get a better estimate of 18 months). (All of that is in the first entry "Sol 6".)
So the MAV has to launch 22 months (at least) before the humans. The mission is 1 month, the return 4 months (if symmetrical, which needn't be the case). So if the overall mission is 36 months the humans get there in at month 31 (and launch at month 27). Thus the MAV has to launch at month 9 at latest. What happens during the earlier 9 months? Perhaps some supply (food and other materials) missions go then. And maybe some go immediately after. So in that case there'd be plenty of food around (he'd just have to go collect it by himself).
On the other hand, if it only takes 4 months for the supply ships to get there maybe they wait until after the MAV is there and working and only then send the later 13 missions - to get there before the humans launch. 989
Why waste them if the MAV face-planted and busted up? So, launch the MAV at time 0. At month 4 it lands successfully (or not). By month 10 it's generated 6 months of fuel and is still going strong. Now you have a full year to launch 13 more missions and have them all get there successfully before the Ares 4 leaves earth orbit. So maybe the food isn't there yet (since the MAV arrives when <PERSON> does the first food shipment on this schedule wouldn't arrive until he's been there 10 months).
(I realize this isn't an answer, as it is inconclusive. But its too long for a comment ... and maybe someone else can work on it and improve it. And check my math. And reconcile this with <PERSON>'s comment that he has 4 years to survive, while the entire Ares4 from start to finish ought to be 3 years.) 989