The confusion might be around the term "patch". These can be sometimes be simple diff patches. Or they can be multi-step processes, including reboots, all wrapped up into a single "patch".

For example: https://www.tuhs.org/Archive/Distributions/UCB/2.11BSD/Patch...

I recently updated from patch level 462 to 469 (the most recently patch available) and even with excellent documentation, it was an involved process. If you look all the way back to the first set of patches (https://www.tuhs.org/Archive/Distributions/UCB/2.11BSD/Patch...) there isn't even documentation for the most part. Some diffs, some random tar files, and some "Remove everything above the #! /bin/sh line." patches.