There's definitely hundreds! Where I'm from, people thought there might be around a hundred and fifty of them, but there's trainers here with Pokédexes showing up way more Who knows how many there really are?

It's got to be the same with magic, right? Like you said with the two mages meeting and knowing some of the same things, but knowing different spells too. You can try putting them all in a book, but I bet even magic buffs find new spells all the time.