John,
I meant the mag would have been tossed when the pistol was first disabled, not when dug!:o

The pistol appears to be in "as found" condition. Unless it was found more than once, I think no one tried to remove the grip screws, otherwise they most likely wouldn't be there anymore.

Maybe... But if it were being used right before it was dropped/lost, what would have kept the grips from falling off? If the safety lever had broken before loss, I can envision using the gun without it, but my guess is that someone tried to take the grips off in order to loosen the mag, and probably forced the lever, as well, just trying it out. Without more info, we simply do not know.

I'm thinking on the line, those parts (grip screws; safety lever) corroded away during all this time for unknown reasons.

Maybe a chemist among us could have an hypothesis on the whys.

Smaller pieces will corrode quicker, as they corrode from all directions- till nothing is left.
The safety lever is quite thin, so same principle; could also be the pin or the ledge that holds it in could have disintegrated and let the lever "fall" out when touched.

I'm afraid this is another one of those puzzles we will never know the "real" answer to.

But the picture clearly shows that different parts/metals/treatments show different amounts of corrosion when buried. Great picture.

Keep in mind what I posted above, as well. These parts may have been exposed to the elements, while the balance of the pistol was covered in mud. How it lay for so many years would have influenced what rusted away.