To understand these bits, it helps to define their components. Reversible bits must be disassembled between coping and sticking cuts. Shims are used to adjust the fit. Combination bits are raised or lowered, depending on the cut. They may also be shimmed.
Matched sets have separate coping and sticking cutters.
No shims are used. The coping cutter leaves a stub tenon as deep as the groove for the panel. For a tight-fitting joint, the bits must be machined to high tolerances, and this isn't always the case. If you can't get a joint to fit after much trial and error, contact the manufacturer and see about getting a replacement. All of these bits require set-up time.