I have had my Ambien CR prescription refilled with a generic but have received 2 different pills that are both identified as Zolpidem Tartrate ER (C) 6.25 mg. The prescriptions were both filled by my mailorder pharmacy. 1 is a flat, white,round pill with only marking - A2. The 2nd looks more like the original Ambien CR - same sort of rose color with marking ZCR. Are both zolpidem tartrate ER (C) 6.25 - maybe made by different manufacturers?