Coffee ages on two separate clocks, and the words on this page belong to the slower one. Current crop, also called new or fresh crop, is green coffee from the most recent harvest at its origin. Past crop is green coffee from the harvest cycle before that, roughly a year or more behind. Both terms describe the unroasted bean sitting in a sack, and they have nothing to do with the roast date printed on your bag, which tracks a much faster deterioration measured in weeks.
The difference in the cup is a trade, not just a decline. Kenneth Davids, in Home Coffee Roasting, describes the pattern from decades of buying green: as coffee ages in decent storage, acidity slowly falls and body rises, so a current crop lot tastes brighter and lighter than the same coffee held a year longer. In poor storage the trade turns into plain loss. Heat and swinging humidity make coffee fade or go baggy, a flat, faintly ropy taste named after the jute it travels in.
The boundary between the two terms is soft. Maxwell Colonna-Dashwood's The Coffee Dictionary makes two points buyers should keep. First, exactly when a coffee becomes past crop is not clearly defined, and origins that struggle with drying slide there faster than origins that dry well. Second, the line has moved: sealed storage liners such as GrainPro, now widespread, hold green coffee in good condition well past what jute alone allowed. There is even a market that runs the other way, since Monsoon Malabar and Old Brown Java are deliberately aged for years and sold on that basis. Age itself is not the sin. Unacknowledged age is.
That is where a buyer actually meets the term: in disclosure, or its absence. Roasters buying green see harvest dates on contracts and will usually tell you a coffee's crop year if asked. Retail bags almost never volunteer it, and a faded past-crop lot can hide comfortably behind a recent roast date, because roasting old green produces fresh-smelling, quietly dull coffee.
What these terms will not do is help you judge the bag on the shelf, since the harvest year is the one date retail packaging reliably omits. Keep the two clocks separate when you think about freshness. The harvest clock runs in years and belongs to the green bean; the clock you can actually manage at home starts at roasting, and how long coffee stays fresh depends on the format you buy it in.