You don't need to be a coffee scientist to get the signal. Here's the low-cost method I recommend to anyone who asks:

• Buy from roasters who control their own supply chain. Small-batch spots in Brooklyn or Queens often roast-to-order. They'll tell you the date without hesitation.
• Check the roast profile. Light roasts have a shorter shelf life than dark roasts. So if you're buying a light roast, the date matters more.
• Use your nose. If the bag smells like stale bread instead of coffee, the date is a lie.
• Look for a 'roasted on' stamp, not a sticker. Stickers are easier to fake.

That last point might sound paranoid, but I've seen it happen. A sticker can be printed for any date. A stamp is usually applied at the moment of packing.