The gashes don’t look like much:
Not even from the side:
When they happened, I knew where to look, because the Kevlar-belted Primo Comet had two conspicuous bulges surrounding debris jammed between the tread and the carcass along the sidewall: the gashes were wide open!
Much to my astonishment, the tire hadn’t gone instantly flat.
Some screwdriver probing in the leftmost gash produced this nasty glass chip:
AFAICT, the smooth side slid over the internal Kevlar belt as the edge sliced between the rubber tread and the carcass. I think the top entered first, with the somewhat crushed end hitting the pavement on each revolution:
The other gash emitted a somewhat smaller chip.
I rode over something crunchy, most likely the remains of a beer bottle, in a shaded section along Rt 376, and we stopped a few driveways later to diagnose a once-per-revolution thump from the front tire. The tube still wasn’t losing pressure, even after extracting the glass, so I continued the mission; it was a fine day for a ride!
I later filled those gashes (plus a few others) with silicone rubber to keep grit out. It’s surely a feel-good gesture, but maybe it’ll help the tire reach the end of its tread life.
You can judge our “riding environment” by the tire’s condition …
The Smell of Molten Projects in the Morning 
Green glass… possibly Rolling Rock.
https://drizly.com/rolling-rock-extra-pale/p4287
A perfect match!
Speaking strictly as a bicyclist, I like plastic bottles a lot.
So, in your opinion, is the shoulder debris getting worse, getting better, or about the same? Have you gotten to the point where there are no other protective measures left to try? What comes after kevlar?
Definitely worse! The amount of shattered glass suggests drinkin’ while drivin’ has once again become a thing.
The combination of Schwalbe Marathon Plus armored tires and Michelin Pro-Tek goo-filled tubes on the rear has given us nearly a year without flats, apart from the recent slow leak in the garage. The front end is so lightly loaded most chips don’t get into the tread, so a Kevlar belt suffices.
The rear wheel weighs more than your entire bike, but … [sigh]