Homebrew TWL Menu ++ - Anti-piracy patchs name

[SombrAbsol]

Hi there!
Out of curiosity, I'm looking at the anti-piracy patches on the TWiLight Menu ++, and I notice that the patches are named like this (for example):

TCME-7044.ips
IPGS-AC63.ips
CDOK-FBA1.ips

I know that the patch name starts with the game id. But I don't know the name of the other four digit code at the end of the name. I have looked for what it might be, but it is neither CRC, nor SHA-1, nor SHA-256, nor MD5.

Do you know what it is?
Thanks in advance!

 

[RocketRobz]

It's the header CRC16, located in the DS ROM, at offset 15E.

 

[SombrAbsol]

I didn't know that there was the CRC16 :o

Thanks for your answer!