Hello there,

In NEET these codes are usually used to mention paper codes. Many other compettive exams also use this paper coding system.

This coding system is nothing but to differentiate papers by question number arrangements.

All papers includes same question but their numbering are different.

For example ,You got paper code E1 and your friend got F1, here the question number 1 in your ques  might be at ques no 10 or any other number in your friends paper.

So nothing to worry about paper code , these are based on question arrangement.

Hope you get it :)

Best of Luck.