Whether edges that are hone by someone else, will respond to a touch up on a flat hone, depends on how the razor was finished. E.g. if the edge was finished on a hanging strop with diamond spray, there will be the slightest amount of convexity in the bevel. As a result, the very edge won't be able to touch the hone any longer, and a Coticule on water is not going to straighten the bevel out. Hence a touch-up won't do much of anything, in such cases.
On razors that have been finished on a hone, or on solid paddle strop, a Coticule on water is a good hone for touching up, but only if you do it at the earliest signs of keenness decline. Actually, I recommend to do it as a no-brainer, every 6th shave or so. Even if done too early, those 30 laps don't do any harm. After sometime, you'll develop a feel for what is needed how often. Maybe on some of your razors you'll do only 15 laps every 10 shaves, and on others 20 laps every 3 shaves. If the shave after a touch-up still feels as if it could be better, simply repeat the touch-up before next shave.
It's always a good idea to also spend some extra attention stropping after a touch-up. I normally do 20 linen / 40 leather before a shave, but if the razor touched a hone, I'll do 60/60.
Kind regards,
Bart.