Muscle confusion? Well, there's one answer from someone without a clue. Not just that, but abs and calves ARE the two muscle groups that can be worked daily!
Developing a "set of abs" is dependent on ONE thing- that's diet.
Firstly, exercising a specific part of the body has absolutely NO impact on fat metabolism there. This is referred to as "spot reduction", and there's absolutely no such thing.
As a general rule of thumb, the "six pack" will show best starting at about ten percent body fat. Since body fat (and subcutaneous fluid retention to some extent) is the ONLY thing hiding those abs (unless you're really hairy- LOL), then trimming fat is the best answer.
The best ways to trim fat are a diet consisting of mostly whole foods. Avoid processed foods, and eat your vegetables raw, when you can. Whole foods and raw foods stimulate peristalsis. This is the mechanical grinding and mixing with gastric juices.
So, to be sure, and from a licensed Certified Master Personal trainer, diet is THE key. Toning the muscles through exercise can help, but it will not get you abs!