On the WNW website there is clearly visible, that the old decals are printed by cartograf.com in Italy (this is visible on one border in small letters). Those are simply the BEST decals available world wide, but don't seem to be cheap.
One example from the WNW web site:

You mention Eduard decals, the highest price range (limited editions and some Profipacks) are printed by Cartograf too, others (e.g. cheap Weekend editions) printed by Eduard themselves. The latest editions of those are very nice.
I never had any issue with a Cartograf decal (also from Revell kits).
So I guess the problematic sheets are NOT printed by Cartograf? Could you please check?
If this are also Cartograf ones, that they have really a production problem.
Cheers,
Frank