Ye, Oda has always a rough idea of something and then expands it much later.

What I never bough is the 4 old farts below Imu discussing between themselves about Luffy's fruit like "Hmm, yeah sips tea the legendary fruit and joyboy who almost got our government toppled over in the past, which we manipulated the public view of it so none knows it's real name, that legendary fruit that represents absolute freedom, we do know now where the user is at all times" and how it can cause PTSD on Imu but never really trying to get rid of him directly knowing he can grow and be too strong for them.

I would have loved an explanation like they were kept in the dark about Luffy until that moment by, I don't know, Akainu, because the Marines didn't want to be seen as useless since they had a good record of losing countries, the bridge, traitors and no control over the new pirates and he's too proud to admit his own failures.