The lists probably haven't been updated yet.
If you buy one now you should be able to claim any credits available for the quarter you purchase the car in. The IRS master list is a guide only - it doesn't show the 2016 Volt either but if you find one of those still on a dealer lot it would also qualify. CARB is a different story so you'll have to check with them.Check again on Jan 1, 2018 for federal credits. As for CA, I am sure it will be added around the time GM starts shipping 2018 Volts, if they continue to qualify.