I think cognac has no vintage value unlike wine. Those you mentioned are mostly cognacs and they do not aged like wines. I doubt they are labelled vintage. Wines are valued by the year they are produced. Sometimes the grape harvesting is good or bad and that determines the value. For example when I was in Langkawi in 1997, I bought a few bottles of 96 merlots for RM40 each and now they are selling for almost RM280 per bottle and it is getting scarce.
That's why you don't have cognacs bottled with year on the label.

Anyone out there can clarify ?