Finally, an article by Ben at Hodinkee on Ref.6240 SOLO. It’s in English, but worthwhile if you’re interested.

Summarising the main points, “the theory that the original SOLO dial comes from an early Ref.6239 is correct, but the trend in the current market is moving towards an early Ref.6240 also makes it the best. The value has also followed this sort of move without contradicting the period. And best included in Ref.6240, since it looks so good.”

Cf :​ ​​ ​hodinkee.com