These "Developer's Notes", written by the principal PIKT developer, Robert Osterlund, partly chronicle PIKT Changes, and partly report old news. They will also provide additional examples and give you some insight into day-to-day PIKT operations.
Developer's Notes will typically, but not necessarily, chronicle the events and circumstances leading up to each release. So, for example, Developer's Notes 1.18.x describe the 1.18.0pre (beta) releases, and events following the release of the immediately previous version, 1.17.0.
Note that older developer notes are not irrelevant or outdated. Most of the things discussed in older notes still apply to the latest PIKT versions.