I don't think there was ever an explicit policy regarding that issue in FD scale.
Because I'm the guy here who's never shy to use large volumes of someone else's FD work (to create even larger volumes of new work), plus I'm dealing with FD archives, so I can tell You how I'm approaching it and in these circumstances it rather won't be "the least valid voice in the discussion", but since I'm not an Admin my words have no "official standing" - just so far it was accepted how I did it (but tomorrow Admins may decide otherwise).
Closest to any policy was an implied adoption of the rule that is in use in regard to SB Uploads: "new work has to offer a real improvement over previous one".
IMHO a "real improvement" can be potentially achieved in 3 areas:
-more accurate representation (if there are scaling or proportion errors, or if just elements are missing),
-higher stylistical quality (sophistication)
-more models/versions and paint schemes/users.
Usually I'm trying to do all of it.
As for the Do-335 drawing, so far it looks very promising. Personally I'd outline flaps, ailerons, rudders etc. etc. moving steering elements in black, of course I'd add the shading on fuselage made by wings and horizontal stabilizers - and probably move a pixel or two in few places, but I wasn't looking too closely on it to tell much.
But as a request could someone please reupload the P-51D Darthpanda drew? For me the files are corrupted when i try to save it and I really want to do a Luftwaffe camo scheme for captured aircraft.
