I am starting to make sense of what you are saying I think.
My values come from this method:
PHP Code:
public function edit($id) {
$this->viewData['booking'] = $this->bookingModel->select('bookings.id as id,status,mode,date,start_time,location,location_zipcode,location_address,presentations_id,clients.id as clients_id, clients.client_name,presentations.pres_name')
->where('bookings.id', $id)
->join('presentations', 'presentations_id = presentations.id', 'inner')
->join('clients', 'clients_id = clients.id', 'inner')
->first();;
//dd($this->viewData['booking']);
return view('admin/bookings/edit', $this->viewData);
}
So my edit view is a get request. Do you mean that those functions set_value, set_input, set_checkbox and set_radio are intended to only work after a post?
So basically when I do have a form I use for edits, that takes data from a call to the database, I cannot use those.

Okay it took me some time but I am getting it now. I thought I could use them here, but that's not the way to go. Thanks for helping me.
May I ask still something though: why do I get a result in my test for the set_checkbox?
Looking at the form_helper, I can see that first all those functions try to get an old value – which is what I was expecting to achieve.
PHP Code:
// Try any old input data we may have first
$input = $request->getOldInput($field);
The set_checkbox seems to find it. Not sure exactly then what happens there?