Don't get overly excited by the 4 month rust. Remember this thing has never been oiled and has been sitting without lubrication that whole time. I should add that it has spent this time in my basement during the most humid part of the year. That is a rust friendly environment.
What happens with all the phosphates coatings, including Parkerizing, is that some porosity is present which needs to be filled with oil. Absent any oil at all, phosphate coatings will eventually develop rust just because they leave some microscopic spots unprotected at the bottom of the pores. There is also a certain amount of free iron in the phosphate matrix that has converted to the phosphate form, and it can oxidize, too.
What my experiment was about was to see how much the acids in cold blue processes actually promoted rusting? I concluded that Van’s and Oxpho-blue do so only very slightly if at all. Most of the darker cold blues use nitric acid as one of their constituents. My hypothesis was that this over-activates steel in the process of growing the blue selenious coating on it. Surface rust or so-called rust-through develops very easily if you aren't very proactive about preventing it on an activated surface.
Hydrochloric acid was in one very old bottle of Outers cold blue, and that not only activates the surface but leaves some ferric chloride in its wake. Ferric chloride, in the presence of water, will etch and activate iron by itself. Drop a nail in some ferric chloride circuit board etching solution sometime and watch gradually disappear.
Rust-free use of the nitric and hydrochloric acid-based cold blues requires that you neutralize the acid (Formula 409 cleaner does this well), rinse them thoroughly, then boil them for 10 minutes in distilled water then get them straight into a water displacing oil for an overnight soak. Brownells Water Displacing Oil is the best I've tried, but WD-40 will do in a pinch. Just be sure you replace it with rust inhibiting oil later. After all this, the cold-blued areas have to be kept oiled, greased, or waxed. Otherwise they eventually develop rust. This is probably what happened to your gun; incautious or uninformed use of a nitric acid cold blue.
Both Van's and Brownells Oxpho-blue can be applied, washed in 409, then simply rinsed in hot water and dried and oiled with a rust inhibiting oil (LPS-2 or 3, Birchwood Casey Sheath, Amerlene Seal). A soak in water displacing oil might not hurt, but isn’t required if you get them dry. They are also more rugged than the other cold blues. I don't yet know how rugged Blue Wonder cold blue and Blue Wonder cold black are? I haven’t tried any rub-away experiments with them.
Nick
