Stans No Tubes

I used the stans no tubes in the Larssen TT for 1 month. I rode these tyres both leisure and racing. I never had a full flat. One day I heard a hiss and seen some of the liquid spray out but it sealed pretty quick. I continued riding with the same tyre and didnt add any more air. Tonight I was changing the tyres for Slicks for a road event tomorrow. Here is what I found inside the tyre with the pressure still around 25psi.
This piece of glass had went through the tyre. The hole sealed when the glass was pushed right through. I only became aware of it when I took the inflated tyre off.

Stans No Tubes works and works well.
I dont know why I havent used the tubless system before.