Class rules state the minimum cloth weight of the main is 6.25 oz. Is this minimum weight the weight of the cloth only, or the weight of the cloth inclusive of (for example, in North terms) a high molecular weight urethane "OLY" coating. In other words, do the class rules allow the use of a sail cloth under the 6.25 minimum, if the additional weight of the urethane (or the like) coating adds enough weight to meet or exceed the 6.25 oz requirement?

The class measurer I'm sure will weigh in here but it has always been based on the cloth weight, not the weight with the finishing coats. This provides a consistent baseline that all sailmakers may build to. Class rules specify dacron (or other trade name equivalents) so the associated cloth weights are very well defined for the sailmakers to build class legal sails.