FWIW, I have had 3 PRO’s come thru my place that I fixed up and sold. All three had comp carbs w/o adjustable H circuits. They had a little white plug blocking the H hole. This one is mine and has been ported, so it has an adjustable H circuit. However, the air filter cover remains sans adjustment pic for the H screw. If they came with adjustable carbs, I haven’t seen one yet. View attachment 1149403
They certainly could have been produced with both I suppose. The above is what I have learned from my experience.
It's an EPA thing. I believe the early USA pros came with the WT-426. IPL shows the for Canada.
The covers swap. You can make a WT-194 a compensator swaping covers, or a WT-426 non-compensator.