For example, if there is a seasonal spike for the past 30 years of X%, but a yearly decline over the past 5 years of Y% they aren't going to buy for the season like they did 30 years ago. It's just common sense when you look at it, but it's a bunch of number crunching none the less.
While I don't sit on Ilford's or Kodak's financial advisory committee (1), so I cannot speak with any real authority, I'll bet you an unopened roll of K64 that they see less volatility in their silver price than the spot market.
(1) I'm not sure my wife even likes for me to sit on our household financial advisory committee!!