In reference to your FNL archive products, when we retrieve a map corresponding to a specific date do we get a model predicted field or an actual one? Interpreting the caption in the lower part of each figure we would be inclined to think we are dealing with an analysis. When one looks at the caption on the left side, on the other hand, an initializing date is indicated and the suspect arises that we are facing a prognostic map.
Most FNL fields are model output analyses. The exceptions are 6-hour accumulated precipitation and 6-hour average flux values and cloud cover. The plots give the forecast hour at the bottom (+0 or +6). See also Table 2 of the FNL README file at https://www.arl.noaa.gov/archives.php. The label on the left side of the map, which gives an initialization date, is not correct for our archive files. It's just giving the date/time of the 1st record in the file. Historically we've used the same plotting program for both forecast and archive files and haven't changed this labeling.