I created a table in Excel that had dates between 1/1/1901 and 12/31/2101 that can be joined to a standard date value (no time portion of a date). The table has 4 columns that convert the date to numeric values of the Year (1901-2101), the Month (1-12), Year with Decimal Month ((Month - 1) / 12), Year with Decimal Day of the Year (Day of the Year at midnight / total days in the year).
I imported that table into ArcGIS as a File Geodatabase table. Excel dates cannot be any earlier than 1/1/1900 and I needed dates extending back to 1890. To deal with that I copied records between 1/1/2090 and 12/31/2101 (so leap years would align) to a new table and subtracted 200 from the year component of the date and did a similar adjustment to the other date values. Then I appended the original excel import to this new table so the dates would have ordered ObjectIDs.
This table can be joined to feature classes that cannot have their schema modified. Additionally, by joining this table to the date I want to symbolize I can be sure that all dates possible in that date range will be accounted for in the symbology, even if they are not currently present in the data. The numeric values in any of the 4 fields can be used with Quantity style symbology without maintaining a separately calculated field. I can use Categorized Symbology with the Year or Month fields if I want (although I would have to add values not actually in the data in this case) and I do not have to maintain a separate field in the feature layers being symbolized that has to be separately recalculated prior to redrawing.
Other fields could be added to the separate date table easily, like day of the year whole numbers, or numbers/strings showing the YYYYMMDD style of date for sorting, to support any other symbol groupings by date that may be required without constantly modifying each separate feature class.
If I did take the separately calculated field in each feature class approach, I would use Attribute Assistant to create a DynamicValues table rule that would maintain the field value during editing.