To help find and identify my old account, I sent Blizzard my telephone number/s and addresses I’ve had for the past twenty years. The answer to the ‘secret question’. Two invoices from Blizzard, one ELEVEN years old. The names, classes and realms of some of my main/est toons. I described a techical issue re: syncing that occurred with my account many years ago–the Blizz employee at the time said it had never happened before. Not that they’d keep the millions of tickets they’d received, but yes, I even gave that a shot as an identifier. Lost my authenticator a long while back, but felt nostalgic enough to want to play a nearly 20 year old game again this week. They want to have my driver’s license before I play.
Yes, they want to know that you are the registered account holder. They won’t just give the account to anyone who asks. They try hard to ensure it goes to the actual person listed on it.
You can read about the requirements for Govt issued ID here. It is deleted after the ticket is resolved, so if an issue comes up again you would have to re-send it.