El Nino Watch
The ERA5 history is fetched in decade windows, one per hour after start-up. Until every window is stored, the numbers that need a missing month are blank and labelled "loading, not estimated".
Koh Samui watch
The daily ERA5 data since 1950 (about 28,000 days) is downloaded in decade windows, one window per hourly run and never in the first five minutes after the server starts, so the shared Open-Meteo quota is respected. The status line at the top of the page says how many months are stored, which windows are still pending and the last day with valid data (ERA5 lags about five days).
While a window is pending:
Nothing is estimated to fill the gap. Once the windows are in (about eight hours on a fresh install), the page is complete and only the current year is refreshed, once a day.
A green "complete" state with a recent ERA5 date is the normal case. "Loading" with a list of windows means come back later, or check the Sources page (source samui_era5_history).
A blank cell is a promise: the page would rather show nothing than a number that was not computed from the data.