please do not use food oils! I recommend Ballistol because it mixes with water and allows the water to evaporate from the solution; a lot of oils will simply seal moisture below them locking the fox in the henhouse. Store the razor in a very dry place and if in a drawer or box there should be desiccants nearby.
Let the oxidation you see be a clear and emotionless indication that the care you were administering (which you found in nobility to be good) was insufficient. Rust never sleeps and there's no such thing as defective carbon steel for developing oxidation. That said, as you can see, file jimps (the little ridges on the tang) certainly create positions on the blade where pro-oxidation conditions are easier to develop. But care for it correctly and there is none to worry.
As for the razor having edge issues and arriving to you with the seal breached via a purchase from Amazon, that should not happen - if the razor is to have been opened for further post-factory honing/inspection/etc., the listing should exhaustively detail this condition. As you imply that it did not, I would in your shoes at least reach out to the vendor and ask about it.
An edge is as fragile as aluminum foil, there could certainly have been injury to it during your regular stropping or use on the face when the administrator is inexperienced (one big stroke at too steep an angle upon poorly stretched and lathered beard can definitely make tiny chips in the blade!) A lot of water's gone down the Hudson in this regard since you've bought it, so who can say with certainty if that was as it arrived?