Antiqorum (one of the worlds most prestigious watch auction houses) date several watches with newer serial no. than his newly aquired Vacheron if we look from their archive we see;
Vacheron & Constantin, Geneve, No. 369894, case No. 261174. Made in 1914. Very fine and extremely rare, early, 18K yellow gold gentleman’s wristwatch with winding-crown at 12 o'clock. C. Three-body, solid, polished, case back bearing the initials: "J.B.", flat bezel, concave lugs, top winder.D. Matte silver with painted bâton indexes and Arabic numerals, subsidiary sunk seconds. Yellow gold "Epee"hands.M. Cal. 11 3/4 ''' gilt brass, 17 jewels, straight line lever escapement, cut bimetallic balance, Breguet bal-ance-spring.Dial, case and movement signed.Diam. 29 mm.
So this one is 369 from 1914, my friends' is 349.
And here is another one from 1908;
Vacheron & Constantin, Gen?ve, No. 341034, sold in 1908. Recased in the 1940's, case No. 209893.Fine and rare minute repeating, 18K yellow gold gentleman's wristwatch.
C. three-body, solid, polished, overhanging teardrop and curved lugs. D. matte silver with applied yellow gold indexes and Arabic numerals. "B?ton" yellow gold hands. M. 11 ''' rhodium-plated, "fausses-c?tes" decoration, 19 jewels, straight line lever escapement, cut bimetallic balance, adjusted to temperatures, Breguet balance-spring, repeater on gongs by means of a slide on the band.Dial, case and movement signed.Diam. 36 mm.
Which being a 341 is not far off my friends VC 349
So this would probably make my mates watch made in 1908 and completed or recased in 1920's, which is very exiting, because it's the difference between it being worth 2,000 swiss francs or 100,000 , which was initially why I was so sceptical.
Further reserch has to be done, I will keep you posted as to the results, but we are now both very optimistic, but I must stress my friend is not selling the watch yet so please no-one ask, he is very pleased with it.