A1 coach is 97 make, A2 coach is 2014 make. during reservation if possible prefer A2 coach. However as S4 is next to A2, one side of doorway and toilets will be blocked by unreserved or other class people. Coach attendants and pantry people tried their effort to clear the people, but in vain. gypsy kids were freely running inside and TTEs' were least concerned (as experienced on 23rd Dec in Andhra).
Kindly also note B6 and B7 is placed between A1 and A2 (as experienced on 22nd Dec from NJP). Its S1,2,3,B1,2,3,4,5,A1,B6,7,A2,S4 and so on.