En el 6105-811X existieron esos dos modelos. Existe una tabla que establece dependiendo del dial, y de la fecha si tenían un tipo u otro. El redondo es el primero, y el de texto recto es el último. No obstante, se han encontrado del segundo tipo más antiguas que algunas del primero.
Copio un estracto de un post americano:
" all 6105-8000 and 6105-8009 I have seen were made 68 or 69. The earliest I have seen were May 1968. There may be some made earlier, and maybe some made 1970. I do not think any were made later than 1970.
They all have the circlular "classic" caseback stamp, and dials are "Japan 6105 -8000t" and all have 6105a non hacking movements. Of course some "franken watch" variants may exist, but I think this is how they came from the factory.
The earliest 6105-811x's I have seen are July 1970. 6105b hacking movement, circluar print caseback, and dial, caseback stamped "proof" I believe one other forum member has one like the one in this post.
The latest "classic" circular stamped case back I have seen is February 1973. This has the "resist" caseback and dial "Japan 6105-8009T" All -8009T dials I have seen say resist.
The earliest "line by line" non classic 6105-811x caseback I have seen in august 1974, I don't know exactly when change in caseback stamp was. The latest 6105-811x I have is november 1975, but I think they were made as late as 1976.
So, quite a number of variants out there for a "completeist" in the 6105 divers
6105a movements
stage one 6105-8000 (proof 8000t dial, proof caseback)
stage one 6105-8009 (proff 8000t dial, proof casbeback)
6105b movements
stage two 6105-8110 (proof 8000t dial, proof casbeback, "classic" print)
stage two 6105-8119 (proof 8000t dial, proof "classic" print case back)
stage two 6105-8119 (resist 8009t dial, resist "classic" print case back)
stage two 6105-8110 (resist 8009t dial, resist "classic" print case back)
stage two 6105-8119 (resist 8009t dial, resist non circular "classic" print case back)
stage two 6105-8110 (resist 8009t dial, resist non cirucluar "classic" print case back)"
Mi opinión es que dependía también de la factoría, además de la fecha de fabricación.
Respecto a la pregunta sobre las Tropic, obviamente la que mejor queda es la de 19mm. Que las hay aunque son muy difíciles de conseguir...
Respecto a las otras, para el modelo normal de agujeros pequeños, quizás es mejor la de 20, ya que es más blanda y flexible, y apretando un poco no queda del todo mal.
Para el modelo de agujeros grandes es mejor de 18mm, ya que al ser más compacta la goma, aprieta mucho una de 20mm (y casi no gira la correa). En la de 18mm sobra muy poco, y queda bastante camuflado con las asas.
Saludos