I see what you are describing, and I agree that that's a possibility. But I suspect that the latch is just stuck. It would be odd for a guy to spend so much time building such a beautiful rifle, including hinges and door panel, and then rivet the door shut. Hidden latch buttons can get stuck just like regular simple latch buttons, and that makes it all the more difficult to figure out the situation when something isn't working.
I realize that you are selling it, so leaving things as they are may be the best plan?

If it has a latch but the latch is stuck, then pulling the butt plate off might expose the latch. Pulling the toe plate or the box would be the next options in a search if one needed to continue.
I don't need any more rifles, but I like this one a lot. I hope you get a good sale.
Whetrock