Bob, the biggest tell is that Landeron didn't produce the movement until after Heuer had merged with Leonidas in 1964. At some point during 1964, they stopped signing the bridges Ed.Heuer & Co SA and went with Heuer-Leonidas instead. By the time Heuer used the Landeron 189 in 1966, no bridges had been signed Ed.Heuer for the best part of two years - that had in fact ceased to exist as a legal entity, superceded by the merged company. Whilst they may have used up some of the existing Valjoux bridges, there is no way a new movement would have had the "old" bridge.

Heuer pointed out in advertising that the '66 Carrera 45 Dato was their first chronograph with date window too, so it's not like another, "lost" watch would have preceded it.