Funny that you mention this - I just picked this up today: I think a rare one - MIAG with just the "4" stamp and lot number: "9".
No rust - panzer grau paint with "Luftwaffe blue-gray" mixed in on top.
Price was very good too (around 15 EU).
I have a few too Bob!
The MIAGs are unique in that in 1944 they dropped the full date and only stamped them '4'