There are links at the end of each page and he does literally upgrade the same install up to the last.

It's a great read but...

I run Debian since version 1.1 (not 11 but 1.1) or so (and I was using Slackware before that) and I always re-install my entire system from scratch. I never ever upgrade.

YMMV but to me if you upgrade if either the old (with all your configs) or the new version has a security exploit you are toast. While if you re-install from scratch, you're only toast if the latest version has a security exploit.

Also it helps to keep my skills sharp: I'm forced to re-install and re-configure everything and I like it. I use the opportunity to enhance my shell scripts, to learn new stuff, to do a few things here and there in a better way, etc. FWIW I'm not on Trixie yet (except on one NUC): I need to switch one of these days (and I won't upgrade).

Now the usual disclaimer... I don't claim my way to be the way: to each his own bad taste.