The "allocation period" does not necessarily mean that your car will be coming in that month. If I understand correctly, it has more to do with the dealer's monthly allowed allocation. Think of it as a draw against commission. They weren't supposed to get any more WRXs this month or next, so your order takes one away from them in their 2013-01 allocation. My order's allocation month is November, but my car will be at the dealership within the next couple of days (currently "at railhead"). Somebody ordered a Crosstrek the day after I placed my order, and they got a 2013-01 allocation month as well, but their order will arrive late October/early November. It has little to nothing to do with when your car will actually arrive.
My order also showed "month of November" for the estimated ETA on the same day that I ordered (8/15). I don't think that has anything to do with it being built (or not) already - it's just a system-generated estimate. I think it took about 3 weeks to change to an actual date ETA. Just buy a bunch of parts and accessories while you're waiting. It helps ease the pain.