This is supposedly not the case on lighters made after 1984, but I'd like some more confirmation on this. Older Ligne 1 lighters made before 1984 have an automatic gas shutoff when you open the flint chamber. Older lighters will almost always have the older large square dupont emblem with 'ST Dupont' spelled out at the bottom and the circle with wings above it. They also tend to have shorter 6-digit serial numbers rather than the 7-digit ones found on newer models. The first thing is that older duponts tend to say 'de Paris' rather than just 'Paris'. The real question is what time frame each of these elements indicates.

I've not found other guides out there about this online, but I do know that there's ways to date a dupont lighter.