So the procedure is like this........
They will nominate 50 apps upto 23rd March ......obviously the best among them.......
But after that, means upto 10th April they will again nominate 50 but this time they will also consider the apps in the reserve pool (from 6th to 23rd March).....so if your application is received on say 17th March and your profile is not better among the apps received upto 23rd March, but better than second group (apps received upto 10th April)......then you will still get Nominated ;D ;D ;D
And your nomination is considered as one of the 50 nominations of second time period....
Similarly if your profile is still not better than second group but is better than third group(apps received from 11th April to 28th April) you will again get nominated....
So this justifies first cum first serve basis and a fair selection also, opening all the applications.......
And those who got pre-screening e-mails, means they stand somewhere in the group and have handsome chance of getting nomination......
But those who neither got pre-screening e-mail nor the nomination.....they are in Reserve pool....