Do not put matt varnish onto the windows they will cloud up! If you want them to lok like glass give them a coat of clear otherwise just mask them before applying the varnish! You will find that the vinegar will have no effect on a set/ dried decal the silvering that you mentioned is as Bunkerbarge says the surface was not smooth / glossy enough for the decal to adhere properly softening the decal will not help remove the air from underneath only a wetting agent could do that and again only if the surface was very smooth !!! but hey we learn something new each day and we have all done the same dont let it put you off as the next one will be even better
