I'd suggest you start with a blank slate and re-read the unicot and dilucot papers on coticule.be (the other stuff on there is also very interesting, by the way) and start with doing only unicots. It is a much more straight-forward method and you'll result with an edge identical to a dilucot edge and if it is impossible for you to get a good shaving edge doing unicot than it will definately be impossible to get a good shaving edge doing dilucot on the smae stone with the same razor.

unicot
dilucot

Strange to hear that unicot doesn't work, because I've done that quite a bit and have not got one unsatisfactory result.

Please note that for a coticule to work (and logically I assume for all other types of hones) the bevel must be set properly (I use the thumb pad test, looking for an edge that really sticks to my wet thumb).

Also note that coticules on water alone do not add sharpness, they only polish the edge, adding smoothness. All the sharpening of the edge has to be done before using water only.

I am inclined to believe (along with a fair number of very experienced coticule users) that there is no such thing as 'bad coticules', only 'different coticules' that can demand quite a wide variety of approaches (mainly in doing dilucot, though). That is, unless we're talking about a coticule with minor inclusions that come loose while honing; they will just damage your edge. I have five coticules, all different strata and only one that is unusable as it has such inclusions. You can see these inclusions with the naked eye even in a slurry, in mine they look like grains of sand.

Some coticules are less suited for establishing a bevel than others, but if the bevel is set on another stone there should be no problem.