I haven't been to Samana/Sanchez for 6 years, so am not current. But during all the years that I lived in Samana, there were always guaguas from Sanchez to LT that met Caribe Tours in Sanchez to see if there were persons going to LT.
I doubt very much that those guaguas no longer meet the buses looking for LT passengers.
Tourists going to LT are much more likely to travel by Caribe Tours than they are a local bus.
Can someone more current on Samana/Sanchez than I am tell the OP about guaguas from either Sanchez or Samana to LT?