Success rates with healed seams are low for me on a lot of material. Texas rock with seems has been holding together well for me lately.
I've heard the material filling the seam is way stronger than the rock itself,
Here's two bifaces made from consecutive slabs off a middle texas rock, this point was made from the one on the left. The layers of material changed drastically but the healed seem continued through the layers and played out before it reached the far side of the second slab