James my impression is that there were quite a few changes made over the years to the pre-WW2 Haenels. I have a couple of Model IIs that were made about 10 years apart and there are numerous differences. One is an export model the other domestic but the differences are far greater than you would expect. I notice the cylinder cap on Graham's model I is different from most pics I've seen of this model. Maybe this was because his was an early model? I heard that all the Haenel factory records were destroyed during the War also, so much info on details like manufacturing changes would probably have been lost.