How does ASCII armored key export work?

How does pgp’s ASCII armor work?

I seemingly have three different public keys:

My old Sandra.asc that I’ve given to people in the past,
my current gpg --export (which matches my notmuch autocrypt headers),
and my Delta Chat autocrypt headers (with a primary key imported from GPG) all look different. They all start the same, almost half of the file is the same. “mQENBF0WUq4BCADKwm0rKxqE3rE” etc etc on for a dozen lines. Then a few more dozen lines, different.

It’s not great that I’m giving out three different keys.
Weirdly it seems to work, as in, Delta Chat can read the mails Notmuch sends and shows the padlock.