DLC region lock issues.

Firstly I apologize for being late to the party when this issue has probably been brought up for as long as the DLC region lock system was introduced. I know Google probably has the answers I'm looking for, but none of them directly answered my queries and so here I am, with my selfish intentions hoping someone could give me a tldr version of it.

I live in Asia and I recently bought a game called Nier: Automata. Was really captivated by the game and so I decided to purchase the DLC for it without actually checking the region code of the game, and tada~

Region mismatch.

Now all I know is that the game is either US or EU version. The disc box itself doesn't have the usual region code (e.g. PLAS/PCAS xxxxx) located at the bottom of the spine. Instead, it's being replaced by seven numbers. After being kindly enlightened by the Customer Support in my area, I found out that the region code (CUSA-04551) was on the disc itself.

At this point, I thought it was the US version. But having read some posts on Google, it says that region codes with "CUSA followed by 12 digits" belong to the EU region. Only problem here is that the region code isn't listed on my disc box spine, which is mentioned earlier. And now I'm confused as to whether this game belongs to the US or EU region.

Any answers would be greatly appreciated because I don't want to make the same mistake of purchasing a wrong regional DLC again.

P.S. If you haven't heard of the game Nier:Automata, I highly suggest you go try it out if you are in for an awesome hack & slash JRPG with a great story telling experience. And if you're having any wrong ideas, I'm not in any way affiliated with the game's production crew but someone just wanting to share "the masterpiece that you probably won't play" with the PS community, with it being a PS exclusive as well.