Polo 6 2012 1.6 Tdi cln engine

[StretchRSA]

Can someone please explain to me what the numbers on top of my solenoid mean. My original injectors have the code ki15 on top of the solenoid and I needed to buy a replacement injector which I did but it has the code kg21 on top but the 03L numbers are the same. My mechanic says I need to buy an injector that matches the original ki15 ones but I'm only finding second hand ones with different codes. Is it necessary to match my original ki15 ones or will any work as the 03L numbers are the same? Also please tell me what this code actually means. Thank you
*if anyone has a ki15 injector to sell please let me know