I think Hellsing was an other case of working on IP that was not complete. Manga run from 1997 to 2008 original anime from 2001 to 2002. So missing significant

I think Hellsing was an other case of working on IP that was not complete. Manga run from 1997 to 2008 original anime from 2001 to 2002. So missing significant part of material from Manga... So with pressure to somehow fill 13 episodes, something have to be invented.