I'm not sure why you want to "stitch" a residential slab. It generally has no load on it and the cracks are not usually structurally related...they are usually drying shrinkage cracks.
If you have a homeowner who is concerned about the cracks, they can be filled with epoxy. If you do that, I would also sawcut some joints in the slab, even at this late date, to take future shrinkage stresses off the epoxy repair. Others will argue the effectiveness of cutting joints at this point; however, shrinkage in concrete continues for a long time, and cracks will widen with time. If nothing is done, the original shrinkage stress buildup that caused the crack will continue (though to a lesser degree)and put stress on the epoxy/concrete bond on the face of the crack. Since you will not know the coverage and depth of epoxy penetration, add the sawcut joints as a precaution. When you cut the joints, cut them deeper than you would for new concrete joints. This will assure a reduced cross section and since the concrete has gained strength, give you a better chance to have the process work properly. I would cut the joints to at least 1/3 the depth of the slab (in new construction, the joints are cut 20 to 25 percent of the depth).
Use a gravity feed epoxy (one with a high viscosity)that will penetrate as deeply as possible into the crack. Since you have a relatively wide crack, that shouldn't be a problem. You can also use an acrylic material such as Simpson's AcrylTie that is normally used to set anchor bolts. This material bonds nicely to the concrete and is slightly less rigid than epoxy.
