No one really knows what they do and whenYOU are right
AOR is acknowledgement however they can start processing as well.
"Started processing/working" shows up in some cases , + BGC >> DM . ifor few which would appear in ECAS no? In most cases they may not write that line as above but jumps to BGC>>DM>>PPR but they dont start working on the same day they send AOR 2 acknowledgment of receipt.