Current I797 is valid until Feb 2016 and the extension was recently approved with a start date of Feb 2016 (all for same employer). I do not have a valid stamping now. Planning to go for visa stamping in Dec 2015 and travel back to US by Jan 2016. Would periods from both old & new I797 would be considered while issuing the visa, so that I can travel back to US in Jan 2016? Which petition to use in DS160 and appointment forms?