The DVL ("Deutsche Versuchsanstalt für Luftfahrt" = German research institute for aviation) was somewhat
similar to the US NACA/NASA. That means, its raison d'être was to conduct research work, often for aviation
companies, but it wasn't meant as a design office. So a design designated as "DVL" may be a private venture of
one of the institutes members, but hardly directly from that institute, I think. So, a a designation system isn't
very probable, I think.
BTW, the text in the second attached pi cture has nothing to do with this design, but describes tests of towed
bombs as weapons against bombers.