I have just been reading an interesting article. There is no mention of the specific bayonet types, but he does mention the change from a.A. to n.A., i.e how the a.A. were refurbished into n.A. bayonets
The a.A. had wooden grips a bit rounded on the sides along the top.... when a factory put the Schutzblech on to change it to a n.A., they changed the wooden grips for new ones that were flat along the top, this way they would be flush with the Schutzblech. The Factory would them also grind off the "ears".
When the Army in the field did the changes they usually just added a Schutzblech, often leaving the old grips and ears on the bayonet.
I assume that means they had to fit the Schutzblech to the grips that were already on the bayonet. In the top bayonet in post 14 you can see a slight concave dip along the spine of the Erfurt 1915, and the Schutzblech is rounded on the side to fit the old a.A. grips that are still on... If one had a factory refurbished bayonet with straight wooden grips (as in the bottom one in post 14) you would not be able to see the slight concave dip in the spine as it would be hidden by the grips and Schutzblech... Erfurt had dips in their 84/98aA as well... maybe it is a throwback to this?
Photos to follow...
I hate to admit it, but I am really becoming interesting in items that have just been laying in a box up until now :-(