@theSLAYER Gotcha, that makes sense. Thanks for the explanation (and all the other resources and write-ups you've made available), it was very helpful!
Apologies,I should've been clearer there, can see where the ambiguity came from.
The shiny Arceus included in the BDSP Shiny dex looks like to be the shiny Arceus variant distributed as part of the pre-order event for Pokémon the Movie: Hoopa and the Clash of Ages in Japan.
The TID (03075), SID (00081), Trainer Name (デセルシティ), and Met Location (Pokémon Movie 15) all match up. However the moves appear to be different.
Moves in the shiny dex entry: Recover, Hyper Beam, Perish Song, Judgement.
Moves according to the distribution event data (see Serebi or your Movie18 Shiny Arceus file): Judgement, Blast Burn, Hydro Cannon, Earth Power.
Again, I might be misunderstanding something, so apologies if I am.
I might be dense and missed this somewhere else, but in the BDSP shiny dex, the Arceus seems to be the Pokemon Movie 15 Shiny Arceus, given the TID and Met Location. But the moves appear to be different. Is that a conversion issue between the origin game and BDSP?