Good question. As in everything related to vehicle ordering, there appears to be no absolutely correct answer, at least as far as Chevy goes.
I have seen posts where a part is available before even the part number, just as I have seen posts where an ordered part has arrived w/o a price, or ordered w/o a price and the price not known until the part arrives w/ invoice.
Sometimes it seems part never arrive (just ask the members who ordered an LTZ turbo in the summer of 2011 and not see concerted regular production begin until November, a full three months after the Sonic started and almost a month after the LT turbo started regular production.
So: good question to which I (nor anyone else) know the answer.
Until the part order can be fulfilled.
Then we all can know the answer.
Laborsmith