Perusing - as you do - and came across this compilation :

📚 The Hitchhiker’s Guide to the Galaxy: A Trilogy in Four Parts by Douglas Adams (sorry - Amazon link - couldn’t find this edition on MicroBlog)

It reminded me of a much older ‘trilogy’, penned by one Spike Milligan - who around book 5 wrote something like

Number 5 in the increasingly misnamed ‘War Trilogy’.