Dave,
You're right, I didn't find any reference to them in the plates. However, I discovered some other things, while looking. First will go to the Trawnik book page 50 where he shows a grenadier reserve with a landwehr cross in the low position and a landwehr grenadier plate with the cross in the middle of the chest. He clearly shows a difference between grenadier reserve and grenadier landwehr. Neither of them has a bandeau.
Next comes the Stubbs book with pictures from page 103 to page 105. I do not like his captions for these pictures. On page 103, he shows a grenadier plate with the cross in the low position calls it a reserve officer and says that it should have been in the middle of the chest based on a war minister order from 1869.
On page 105 through page 108. There is another grenadier helmet with the landwehr cross in the middle of the chest and a bandeau. The caption says. "The reserve crosses was probably attached to the existing helmet plate when the officer passed into the reserve." Yet this is an M15 helmet and that is not how the commissioning/career progression process worked.
Then you come to the Hilsenbeck book. On page 101. There is a grenadier plate with a cross in the center of the chest, but no caption. On page 111. There is a similar plate called a reserve officer. I found no picture of than 87, 88 or PB 10 with a landwehr cross. However, there is a picture of a Waterloo helmet as in 74, 77, 78, 164, 165. That has a landwehr cross in the low position, an FR on the chest and no bandeau.
I'm still looking and have a lot of sources yet to look at busy day lots of fun
