Where is slug revision behaviour documented?

Post slug for say, /about is automagically incremented to e.g. /about-2 then /about-3 and so the URL changes without any warning, while the older about/ remains available. Where is this behaviour documented?

What causes this? How can one obtain a permanent URL?

My setup:
Ubuntu Linux 18.04 (Bionic Beaver)
Ghost 3.36
Database server: MySQL 8.0.23
Web server nginx/1.14.0
Node.js 12.19.0
Certbot 0.31.0

-2 -3 etc are only added to slugs when there are duplicates, that can only happen if you create new posts or pages with the same title (in this example “About”) without manually updating the slug after or by manually choosing an existing slug.

Slugs are unique, you can’t have multiple pages with the same slug. If you have multiple posts/pages with the same title then you should manually adjust the slugs eg about-company, about-shipping etc

Thanks, Kevin. Cannot explain the sequence, but duplicate was unintended.

Is it possible to remove the older duplicate and revert to the bare keyword slug (/about) ?

I presume it’s not as simple as a bit of SQL hackery …