Don't forget that the makers of medical supplies are out to make money. Sell by dates are there mainly to make more money.
Surgeons are correct when discussing their supplies as they will be putting them inside the body. For a FAK your supplies will be perfectly fine in 100 years.
The medications are mostly fine after their sell by dates. Most medications only loose viability as the years go by. There have been tests done on aspirin that was made over 100 years ago. It is safe but it would take more of the drug to do what it is supposed to.
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Although I agree with the fact that the product will probably be fine, the date is not there to make money but to save it.
I've worked in an situation where we were looking at the aging of product.
For anything - whether it's the painkiller in your FAK or the likely-hood that your cam-belt fails - you are using the mathematical probablility that something happens (or doesn't happen). You can predict the rate at which something will fail or become effective over time and then with a customer, industry or legal standard set a failure rate that is 'unacceptable' then work out the life of your product (or set the time and work out the failure rate at that time).
In my line of work (10 years ago!) we were looking at electical cables (for large-scale power distribution). The expectation for things like the cable running things like the national grid is that a cable would have a working life of 40+ years, i.e that only a small amount of failures would be expected before that date - because this cable is expensive to install/repair and consumers don't like their power blinking out.
However, the rate of failures isn't steady - so with cable, if it works first time it will generally last a long time but as the materials age you are more likely to get a failure and that failure rate actually dramatically increases after a certain time but any single bit of cable could still fail at any time be that short or very long. The manufacturing and the life of the product all affect this... a cable out in the sun will get UV damage, in a tunel it won't.
So, to make sure that we could say that less than 0.1% of cable fails after 40 years you are actually saying that in all probability 99.9% of the cable will last longer. At the time London Underground had cable that was over 60 years old and going strong - you just have to bear in mind that as a company we were no longer beholden to our customer because they had chosen to exceed our reccommended life.
For stuff that can injure people we are even more careful. Food, medication and even items like cars HAVE to be safe so that the fail rate is less than single digit parts per million. The human costs if they are not are too high - think of a car not braking suddenly, people are liable to die or at least be very annoyed. That cost translates into a financial cost or risk - for the car, how many millions are paid out in damages or how much business is lost because your reputation is damaged.
So back to the FAK! Your use by date is there to prevent everyone putting what the manufacturer, industry or legislation tells you is likely to be a non-effective or dangerous product in or on your body. Plus Glaxo don't get rich making bandages and they certainly don't want lawsuits all over the place because someone used one after leaving it by the pooper-scooper in your cupboard for 25 years. So it's not about making money or a marketing scam.
Most likely you willbe fine, it will work or at least not harm you BUT do you want to wait until you need it to work for it not to work... It's all down to how much risk you like. I have old bandages but replace medicines, etc because I've made a judgement on the risks of things happening.
