Is there any reason to use an old Blizzard account for WoW classic? I've not used the Authenticator in ages. And if I try now, it simply doesn't notice that it needs to generate a code. Nor does the "manual" option work. I can go the long route of getting it removed, uploading pictures of my ID, but it seems far simpler to just create a new account. The whole point of WoW classic is to restart at level 1 anyway, so what benefit is there to lose?
The chief problems I see are the need to use a new email (no big deal) and a problem with the Authenticator only supporting a single account (but that Authenticator is still optional? So I can just skip it - it's always been a hassle)
A side problem of this authentication issue is that I can't access the Blizzard fora either, as you need the Authenticator even for that.