First of all thanks to Funksammler for all the effort in providing a really informative anwer. I'd like to add that the message forms shown in the L.Dv. 421/2 and the original unused message form in the group of documents photo "...
paperwork involved." are the 1934 DIN A4 form. This form was changed in 1939 to another DIN A4 form - minor changes in font format and the addition of perforations in the dashed line below the first hole on the left side. It's interesting to note that the hole spacing is not equidistant, but, if the top part of form was detached the bottom part could be placed in A4 binder. This might indicate that there was a purpose for the perforations. All the examples of completed forms that I've seen on various sites have not shown that the top part
was removed. In 1941 a new Fern/Blink/Funk message form was printed. This was an entirely different format from the previous ones although incorporating the basic headings.The form was now DIN A5, print a light green color, perforated part at the bottom,and additional info to be entered. I found the photo below at
www.cryptocellar.org ,
Flossenberg Messages. It shows a form printed in 1942 with Ln.Nr. 36082 (Luftnachrichten Number) at the bottom left.This form is dedicated for Funkspruch only and is DIN A4 size, would this indicate that from 1942 the Ln used its own standard message form?
Cheers
ARYEH