I boxed a bunch of iron up when I moved five years ago. Then another move two years later, then another move two years later, and all that time I had that iron in cardboard boxes, separated by paper towels, newspapers, rags, whatever, and before I packed it all away, I put mineral oil on every piece. I am still unpacking that iron and am very pleased with the way the iron looks as I unpack it. The iron that was cleaned, I put mineral oil on it, the iron that was not cleaned I put mineral oil on it.
The only thing that I found thus far is a speck of rust in the word "griswold", down in the depression, and I think that got there because I did not take the care to get mineral oil in the depression. So I am very pleased and in my opinion mineral oil does prevent rust. This is the results of my field test, based on five years of results, so I will say that I know mineral oil is good for five years. ;)