I'm not sure what else to suggest. I guess if I really wanted to be sure, I'd dig a deep and wide pit, maybe 6x6x6 feet, and then probe as far as I could in every direction. With only two pieces of glass and a few teeth, that's about as far as I'd be willing to go into clay like that. If I didn't find any more glass or anything, I'd fill 'er in and have a good sleep that night.
Be sure to keep your shovel clean if you get deeper down, because you might have some of the topsoil stuck to your shovel, and when you pull out a shovelful of clay from deep down, and a bit of topsoil gets mixed in, you're suddenly thinking, "oh my, here's something different, here's some ash or something". Similarly, if a piece of glass falls in from the surface, or takes a ride down on your shovel blade, you might make the mistake of thinking that there's something down there when there isn't. Stay driven but stay realistic. Good luck!
NJ