As long as you get loose stuff off and coat it, it really doesn’t matter much. It gets better over time. Don’t worry about getting it black like new, thats mostly soot and doesn’t add anything. Mine stay shiny iron forever.
Sometimes I even let it spot rust before the first coat and it gets a cool rusty colour sheen. Similar sheen using unrefined rape seed oil. But really any food oil, even olive oil, works great. Google the smoke point temperature of your oil, or just watch for it to puddle and just barely start smoking.
Good luck!