I am pasting this from the Generations v8.5a Help menu.
Custom Dates Entering/Editing a Person's Information / Dates
When you type a date entry that EasyTree doesn't understand to be a "date," EasyTree will display the Custom Date window.
If you made a mistake and need to enter the date again (for example, if you misspelled a month name or made some other typographical error), click the Try Again button.
Save Custom Date
If you want EasyTree to remember your date entry, even though the program can't understand the entry as a "date," then your entry is referred to as a custom date. EasyTree will store your custom date and use the custom date in charts, reports, and lists. To make EasyTree remember your custom date:
1. Type a valid date into the Sort Date field. A valid date is one that EasyTree can understand as a date. The date in the Sort Date field will be used for sorting (date calculations, comparisons, etc.). 2. Click the Save Custom Date button. If possible, try to enter a valid date entry, rather than a custom date. Here are a few reasons for doing this: • Custom dates require slightly more room for storage and slightly more time to display. • If you need to export dates via GEDCOM in order to share your data with someone else, it is likely that their genealogy program won't understand custom date entries. • Custom dates are not changed when you change the format used for displaying dates. (When you choose Dates from the Options menu and set the universal format.) • Custom dates may not read as well in narrative reports.
Examples of Custom Dates
Summer of 69 SeeNotes 1q 1990 Between 1881 and 1882 1888/9 1888/89 Holocaust