Was it before Kelvin was put in 'The Swan'? Maybe the 'resupply drops' were really coming from deliveries from the likes of Ben's dad whilst Kelvin was in there and he wasn't informed of what was going on in the outside world....

Or was it before 'the incident' at the Swan? What's with that anyway?

Well, it had to be long enough ago for Roger's body/skeleton to decompose to the state it was in when Hurley found the van.

And obviously, quite a while after the "incident." In the orientation film Ben saw when he was a boy, it looked like Marvin Candle's arm was already useless.

http://blog.lostpedia.com/2007/05/time-reveals-more-than-youd-think.html

Lostpedia got it narrowed down to December 22nd 1992.