Hi Nicolas,
In general, successful bidded price plus 25% buyer's premium, the watches are not cheap, considering some of the "so-so" condition pieces. So, JLC has done quite well.
I am not surprised at all that the vintage pieces had out performed the modern pieces. Relatively and in general, vintage pieces are cheaper compared to the prices of the current pieces (of course, with some exception of Patek pieces, for right or wrong reason). Further, I believe when you buy vintage pieces, you also buy its history, nostalgia and rarity (ultimate limited edition).
To me, I only take the auction result as a guide, never seriously because there is always a likehood of untold stories and invisible hands behind its corporate veil.
Thanks for your thoughtful post.
Regards
Ling