There is no 1975 Dollar, Half, or Quarter; because the mint operates on the governments fiscal year, and they started the bicentennials a year early. This means the last quarter (Oct-Nov-Dec) are part of 2016. The government only has about a week left of 2015. So in order to have coins for this year, they had to make them in part before Oct 2014.
ATB cone out roughly in February, April, June, September (Bombay Hook was just released the other day), and November.
Shawnee
ATB should begin minting in the next 2 weeks to be ready by the release date of February. That is when the banks should be first getting them, so odds are it will be already stored in the FRB for delivery to bank by February. So by the time the First quarter is relased, they wil have had 5 months to mint, so will be almost halfway done with the fiscal year and probably already be done with the April release quarter before the Feb release date.
This is for circulation coins. For proofs, that comes form San Fran, and they might have an even tighter schedule as many less coins are made, and they could have every proof Quarter for a Mint Set ready before the end of this year. They work on a different process as well, for example a proof coin is struck more than once, the dies are polished more, etc depending on what kind of finish the proof will have.
IF you mean a Mint Set of P & D, the circulation coin mints, then I have no idea how they would have them out before Feb, but it is possible since that is 5 months into the fiscal year, they could long be done with making quarters, and them jsut move onto nickels, pennies, dimes, halves, and NA/Pre$; so the US Mint store may already have ALL next years quarters readily available to be put into their special packaging because the mints are done with quarters already.
That is just best guesses based on what I know about the governments fiscal cycle.