Google's SynthID (which is built specifically for Google-generated images) seems to work even for the final edit. Try sending it to Gemini with the query "Is this image ai generated?"
See here for more info: blog[dot]google/innovation-and-ai/products/ai-image-verification-gemini-app/
Fakes were easier to fake when Google's image generation was heavily woke/DEI biased, with African Roman Emperors or African WW2 SS soldiers :-)
I wonder why editing any image with Photoshop-like tools is considered an AI augmentation/created?
Image editing using tools has been around for many years, but people are skipping it and using different GenAI models to manipulate images much faster and more easily; these provide a completely different set of results.
I would say that you were using the wrong detectors for this exercise.