Identification: G4 original series or What do you know about hoof codes?

[LivioKelem]

This problem struggles me. And it make me angry. And crazy... U know. 
How I can identificate original series pony if i have two/more identifical toys? Like Fluttershy Train Car or Fluttershy Traveling single wave 1? Or Pinkie Pie: 1st, w/train, RC Car or wedding single? Now I have five Pinkies and only one is clear for me: 02491 is 1st Pinkie. But another...
03331
12101
13391
20411
What is that ponies?
Mb you know smthg about hoof codes or smthg else for me?

[Flitter]

The codes tell the production date.
Here is a guide and code converter to decipher
https://www.mlpmerch.com/2014/03/guide-what-do-codes-under-my-mlp.html

[LivioKelem]

The codes tell the production date.
Here is a guide and code converter to decipher
https://www.mlpmerch.com/2014/03/guide-what-do-codes-under-my-mlp.html

Wow! This is awesome, thank you!