... were still afflilated at the time that the DSA was imported. It's just that V&C was marketed in this country as a maker of dress watches only. Therefore, I'm not surprised that they aren't included in the specialty catalog.
As far as the advertisements you show, I think that while still distributed by Longines-Wittnauer, by the mid-1950's the LeCoultre and V&C brands were segregated in their marketing. Earlier LeCoultre ads sometimes showed a few V&C watches, but that stopped around the same time.
Later on in the post there is a advertisement that shows the DSA and also mentions V&C:
So my guess is that the four companies were still all being imported by L-W as late as the mid-1960's, just not always shown together in marketing materials.
The back of the "Mystery" shows the connection perfectly:
Hope this helps,