An observation date and a vintage date answer different questions. The observation date identifies the period being measured. The vintage date selects the information available at a particular historical date. ALFRED's download guide explains both in its output-format descriptions. [S1]

In an observations-by-vintage table, a row holds the observation date constant while columns show values from different vintages. Reading down one column holds the vintage constant and changes the observation period. A row that stays unchanged across two vintages need not indicate a failed download; its value may simply not have been revised. [S1]

ALFRED permits a chosen vintage date even when that date is not a listed revision date. Its list of revision vintages omits release dates on which the series did not change. [S1]

For a historical comparison, record both dates and the selected output format. Initial-release-only output is a different selection from all observations available at a later vintage. Avoid comparing an initial estimate with today's revised value while labeling both merely by their observation period.

Additional source notes
ALFRED's help also distinguishes source release dates from dates used when an original release date is unavailable. Its documentation describes fallback sources for those dates. Record that provenance before using a date as evidence of exactly when information became available.

Sources
[S1] Federal Reserve Bank of St. Louis — ALFRED Download Data Help — https://alfred.stlouisfed.org/help/downloaddata
[S2] ALFRED Help — https://alfred.stlouisfed.org/help