(at around 28 mins) When Danish goes to Rajhans Mansion to kill his father's murderer's apprentice you can see "EZYPAY" poster on the left side of the screen with Mobile's picture in it. At that point of time as per movie even pagers were not around in India it was some years later that pagers were introduced and Faizal comes to know about it and it took some more years for mobile to be known in India.
When Shamshad chased down Definite through the streets of Wasseypur & Dhanbad, auto rickshaws in green-and-yellow are shown, which use gasoline as fuel. This kind of vehicle has been used only since 2011 in India, not in the time as shown in film.
When Shamshad Alam chase Definite on the streets. One can easily see that the vehicles on the road are having number plates with Registration number of Uttar Pradesh-65 which is of Varanasi. Even the public transport vehicles were having the Registration number of Varanasi which is only possible if the location is in Varanasi but the location of the scene was portrayed to be in the state of Jharkhand.
This is because that the scene was shot with the hidden cameras on an actual location on the streets of Varanasi.
Moharram, a Shia rite is celebrated in the Sunni dominated Wasseypur. But the celebration of moharram procession passes from a lot of areas in and around the city, and for that matter a lot of sunni dominated areas also celebrate moharram as much as Shias do.
While 'Faizal Khan' come out of the banaras jail when he is arrested for the first time for having pistol with him during search in train,we can clearly see mobile battery etc not allowed in the right side of the jail door.Since the scene was of early 90's the mobile phone was not used during those days.