In a fit of OCD I changed the field name for one of the fields [from PlaceName to Place_Name] in the attribute table associated with a feature class [so that it matched the field names in other feature classes]. This caused ArcGIS to message me: "FDO Error: 0 [Failed to label layer Marker for class Default.]". Since the only feature class that had had one of its field names changed was "Marker", a dead giveaway.
So (a) the table is still there [right-click on the feature class in the Table of Contents, select Attribute Table] but (b) only newly added [newly as in: since I screwed the table up] features in this class now show on the map. How do I bring the whole table back, please? Oh, I went back to the Attribute Table [catalog right-click on the feature class in the geodatabase, selected properties and then selected the fields tab] and restored the field name to its original. Didn't seem to resolve anything.
Many thanks, indeed ...