Thanks Jan! So, apart from variations WITHIN the model number, eg AS types, and the deeper oil cooler bath, and the gun blisters, (roads, sanitation, schools!), there are only subtle differences externally, unless I'm getting confused! I've got a series of line drawings from 109D to K, but not all of the models within the series, so this helps. It's just that the captions to many photos in books can be very misleading, as we all know!
From Emil to Gustav 6 I don't have a problem, but the later war period has never been my strong point, so thanks again; now all I have to do is figure out how to save the drawings, without saving half the web-site!