I meant "programmed all of it," out of intense sarcasm and jabbing. :p

it's very possible that he did a lot (to the completion of the game we know it as) before it fell under the reins of Igarashi.
But again, the Metroidvania gameplay, experience points and rpg leveling, the game's title,
and the hero himself were IGA's own ideas. As I linked, Yamane said IGA oversaw her score and overruled the rest of the team when they were hesitant about the soundtrack. As IGA said in that EGM interview, Hagihara left early in development, and that's when IGA took over as director and implemented all the changes. There was no way there could've been any sort of completion of the game because he radically overhauled the entire game from top to bottom.
Given what we know from the interviews I've linked, when IGA joined:
- there was no hero in the game, so IGA used Alucard
- no title, so he used X to show that it was originally a gaiden
- wanted to increase play time, so he used Metroid's format
- wanted to help casual gamers get into the game, so he came up with experience points
If the game was at a stage when there was no cohesive structure or even a hero, there was no way Hagihara could've been involved for longer than the early, post-Bloodletting stages.