I created the original Spatie guidelines site three years ago. Last month, we consolidated a few of our subsites to our main spatie.be site, including the guidelines.
We consider our guidelines as a living document. People, teams, and opinions change over time. We don't dogmatically keep following rules we agreed on in the past, but keep challenging them. New experiences lead to new and improved guidelines.
We also used the old site for internal (private) guidelines. One of those was security, which is now publicly available. Another was our server setup guide, which I've turned into a checklist in a separate GitHub repository.