The roast date is the whole test and its absence is informative. A roaster confident about freshness prints it; everyone else prints a best-before eighteen months out.
Rough guide once you have the date: best somewhere from a few days to about a month after roasting for filter, a bit longer for espresso which often wants a rest. Past two months it is flattening out. Past six it is brown water regardless of what it cost.
That one number sorts the shelf faster than any other information on the bag.