Last week, the Labor Department reported that America’s four-week moving average of initial unemployment claims had declined to its lowest level since March 1973.

We also learned that the headline unemployment rate fell to 3.9 percent last month, marking the first time it’s been below 4 percent since December 2000. (Prior to 2000, it had not been below 4 percent since January 1970.)

Based on those data-points alone, it would seem Americans are enjoying the very best of economic times.

Unfortunately, a few caveats are in order.

The size of the labor force shrank by 236,000 people last month, with the overall participation rate ticking down from 62.9 percent to 62.8 percent.

The total increase in nonfarm payroll jobs (164,000) failed to meet expectations (192,000).

Meanwhile, average hourly earnings grew by just 0.1 percent from March to April, and by just 2.6 percent from April 2017 to April 2018.

“Overall, it’s a good report,” JPMorgan Chase economist Michael Feroli told Bloomberg. “Slack is getting absorbed.” However, “the process of that translating into faster wages has been slow.”

Taking a longer view, we should reflect on what April’s unemployment milestone — getting the headline rate below 4 percent — means for our national economic debate.

“Even a few years ago,” writes New York Times economics correspondent Neil Irwin, “getting to an unemployment rate below 4 percent would have seemed an implausible, unattainable goal.”

As Irwin adds: “For Federal Reserve officials and others who shape policy to try to guide the economy, the sub-4 percent jobless rate can serve as a reminder of how little we know with certainty about what the United States economy is capable of.”