There is no approval of I-864 per se. It just goes to show whether your sponsor will be able to provide financial support for you or not. If USCIS finds something missing from your I-864 (like latest tax return), they would send you an RFE for that, or else, you can pretty much assume that your I-864 is okay if you don't hear from USCIS about it.
There are new I-864 requirements for applicants who have interview after Jul 21st, you will need to go to the interview with all the docs asked for by these new requirements.
