They are processing in the combination of FTD & 2nd AOR, firstly they will go according to FTD & then moved as per 2nd AOR.
So that applicant who submits full docs early after his FTD, he will be processed earlier then others.
Checked one instance,
applicant in NOC 1111 whose FTD was 30.3.10 & 2nd AOR was of first week of may,10 he got processing start date as 10.1.12,where other applicant like RKsharma whose FTD is 31.3.10 & 2nd AOR in June ,10 who got processing start date as 23.1.12.
All the best ....Honeyjack