As I understand it, they are not plate numbers, but more like pane numbers. When printed, a sheet is made up of multiple panes. They are cut up into counter sheets you find at a post office. Each pane in the printer's sheet becomes a counter sheet. The Formnummer identifies which pane in the printer's sheet that counter sheet was. So, if a counter sheet shows an error, the printer knows which pane in its printer's sheet is the source of the error.
Below image shows a British Machin counter sheet. At the bottom left is a matrix. It shows that each printer's sheet has 3 x 4 counter sheets. The sheet in the picture was the second pane in the first row of panes from the printer's sheet. As I understand the explanation, your number has a similar use.
The plate number (cylinder number) is the "D1" above the matrix. Actually, there are three of these numbers as there is the colour, iridescent security overprint and phosphor overprint. I think the number in the picture you post is neither a Plattennummer, nor a Formnummer, but
something like the warrant number (0070097) at the bottom right of below picture. It identifies the order from the Post Office under which the printer printed the stamps.
a sheet number.
But, please, let someone who knows something about German stamps provide clarity on the exact relation between "Form" and "Bogen." Above is just how I read the texts.